Hardcore Gamer, and Casual/Mainstream gamer are more about the type of person and the games they support than a level of dedication.
Your casual gamer is someone who wants what amounts to an experience of immediate gratification, and little actual work or thought to be involved for the payoff. By the definitions you (the article writer) are not a "Hardcore" gamer, your a casual gamer. You want your simplistic shooters, and find the "defeaning explosions" to be the payoff. Games like that aren't difficult to figure out and understand, I mean your typical 8 or 9 year old can plug in a copy of "Call Of Duty" and figure out how to play it and get th emost out of the experience, heck, while they shouldn't be there for ratings reasons, you have kids that young getting involved in the multiplayer and annoying people for reasons that generally have nothing to do with their playing abillity (since they can be pretty good at it given the very low demands to actually understand or play the game). Shooters and games like that are generally speaking the same as "Farmville" they are just aimed at a differant crowd, being directed at men and kids, to provide them with instant gratification of the sort they enjoy, where Farmville is generally aimed at a differant kind of equally unsophisticated audience (the typical "Zynga Housewife" so to speak). The games play differantly, but basically amount to very simple experiences that are approachable by anyone, and start handing out the intended gratification (plants growing, or explosions) right from the beginning.
An actual "Hardcore" or "serious" gamer is someone who might play the kind of games above as a form of intellectual slumming, but generally tends to gravitate towards deeper and more advanced titles. The kinds of things that take a lot of effort to understand and play, never mind play well, because they love to experiment with the depth and complexity of it all. While not the only kind of hardcore game, "old school" stat heavy, turn based RPGs are an example of a hardcore game. The kind of thing where some nerd can sit down and tweak numbers for hours and watch how they play out, and gratification and payoff is a slow process... you might have the equivilent of those deafening explosions, but you earn your way there, as opposed to say being handed a gun and dropped onto the most epic battlefield imaginable to start firing out awesome and towering explosions like a machine gun. Your typical hardcore game is one that a casual gamer will look at and say something like "too much boring" before going back to the latest shooter.
It's an entirely differant kind of mentality and set of expectations and the labels serve to differentiate that. Casuals tend to vastly outnumber hardcore gamers and are also easier to produce for, so you see the industry largely catering to them. From a marketing perspective the gaming industry would like to unify the two groups, since there are still a lot of hardcore gamers, but it's almost impossible to do by the very nature of the divide.
Right now there is a tendency for game developers to try and create a games that are easy to play and complete, but have enough depth to encourage a degree of tinkering and mastery. The problem is that when that depth is optional and you can get the full experience and beat the game without it, it defeats the purpose to a hardcore gamer. Basically if some 8 or 9 year old can finish the game, or worse yet play competitively, it's going to be mindless enough to make your typical hardcore gamer lose interest in most (but not all) cases. Just as your casual gamer sitting down with say an old "Wizardry" game and trying to balane the numbers, so they can watch numbers scroll by during combat, is going to lose attention due to it being "boring" and move on for something with more immediate gratification. Especially if real success in the game depends on being able to "play the system" as much as the game, with some bosses and such basically being graduation exercises in showing your either really patient or more likely mastered the game enough to do exactly the right things the right way (oftentimes counterintuitive to the system) to cheeze yourway past... sometimes both patience and mastery together get involved.
Something like say "Gears Of War" is a quintessential casual game. Something like say "Shin Megami Tensei: Digital Devil Saga" (parts 1 and 2) are more towards the hardcore. I've never been a big fan of hardcore shooters, but a few people have tried to do them, and they have failed. An example of an actual "hardcore FPS" would be something like the "Robinson's" games of years past which were as much gruelling survival sims as actual shooters since you needed to master a lot of variables other than just shooting and making big explosions to succeed in the game. Actually your more likely to wind up losing due to disease, injuries, and other factors than from losing a battle when you get down to it. Attempts at that so far never clicked with me, and your casual gamer was more than likely to not even make many attempts and instead decide they would rather go play "Gears Of War" and pwn people with a chainsaw gun... or I guess for the time period, go play things like "Blood" or "Rise Of The Triad" if I'm remembering the competing titles of the time properly.
That said if anyone has read this far, I will say that I don't think "indie" games have anything to do with hardcore or casual, since indie games are developed for differant audiences. You have plenty of casual experiences like shooters, and zombie massacre simulations coming out for the casual "immediate gratification" crowd, but at the same time smaller "indie" developers are where you also still see the occasional development of things like hardcore rogue likes. Being interested in indie games has more to do with how much your interested in gaming, irregardless of the types of games you play and whether that makes you hardcore or casual.