I have never played WoW so I don't feel qualified to defend it in any case. I HAVE played some really broken MMOs, all of which featured microtransactions.
And anyone that says "I really don't care that all these people got to max level in a fraction of the time I did hasn't had the pleasure of playing PWI in the last few years.
They have hyper XP stones that can give you up to 12x regular xp, and they regularly have (like right now) long periods of time where there is a universal 2x xp/drops event. Which stacks with the hyper stones, but doesn't give 24x xp, I forget what weird multiplier it caps at.
And there just so happens to be an instance, with one room, that has a ton of easy mobs in it that you can pull all at once and kill for mass xp. Did I mention that hyper stones can be turned on and off at will? There are limits, but essentially you have a steady stream of noobs or alts that pay coin to have a high level clear the instance, drag them to the big room, they pop hypers for a few seconds and shut them off. Repeat.
So basically there are literally hundreds of noobs that can skip from level 1 to 100 in a day or two, that have no idea how to do anything at all in game. They don't know where anything is, what their skills do, or what any of the jargon is, and sometimes get people killed. I mean it doesn't take all that long to get up to speed in that game really, but lack of experience when its representative of such a large portion of the playerbase as contrasted by people that spent months or years just getting to 100...the groups don't exactly respect each other. To put it mildly.
Then of course there are the cheaters that exploited a boss a.i. in that same instance which made it spawn like a bajillion adds at once instead of 2 or 3 and got to level 105. The game originally was planned to cap at like 150, but they stopped at 105 and made the xp required after 100 to reflect it as though it were still 150. So, it literally takes billions of xp to get from 104 to 105 while its takes only a few million to get from 99 to 100. They had to patch it, as it was so widely known. Being posted on the forums pretty much daily.
Those people got banned for like 5 days, got to keep their levels, and all the perks of being higher level than everyone else will ever see without exploiting similar avenues. This means that they get to have lv 105 req buff items that give them MASSIVE stat boosts for pvp, that if they are an Assassin essentially no one will be able to attack them or see them at all while they are stealthed, and so they roflstomp 99% of the servers.
Now imagine that in WoW, though I'm sure no where near as idiotic in its application, and realize that unlike PWI you are already paying a fee every month to play said game. A game that has not aged well, and whose continued relevance owes in part to it being the last pay to play game out there. Its perceived that just because people are required to pay that it somehow magically makes the assholes go away so you can game obsessively in peace with no blatant P2W cash grabs or ads harassing you.
XBL makes you pay to play too, and how well did that keep the assholes away? Did it stop them from showing you ad after ad? Just because you have to pay for something, doesn't mean you get any say in how that service does business. Aside from not paying for it.
So WoW *may* start having microtransactions, thereby invalidating its image of being the last, honest MMO or whatever branding their players have been giving it to justify the expense. Expect, if implemented, a definite shift one way or the other in the server population.
I doubt very much that it will bring in a flood of new customers, or that they will stop at xp boosters.