I don't know about anyone else, but when it comes to spending money, it's very much examined as a cost/benefit exercise. How far does my money go to keep me entertained? I can buy a new-ish computer game for £25 or so, and I tend only to buy ones that I know I can pick up and play again some way down the road. My purchase of X-COM: Terror From the Deep has, in that regard, given me an awful lot of benefit for the princely sum of £4.
I played M:tG for about three years. This was (more or less) the three years I was at University, when I didn't really understand money. Income and expenditure was managed on a 'well, I have all my savings up 'til now, and I'm not spending vast quantities on booze'. I was also receiving a student loan (where 'loan' means, effectively, 'free money').
To start with, I played with other people's decks, but you can't have pride in a deck that someone else made. I went onto a free online version of the game, and played around with what kinds of decks I might enjoy playing, and then took them offline by buying a mass of deck protectors and writing on a ridiculous number of small pieces of card all the rules. But again, it wasn't the same as exactly owning that deck. Not to mention the fact that I was having a hell of a time trying to make decks with essentially every card ever - the game was too big to really get my head around understand available strategies.
Then Ravnica block came out. I bought into loads of draft tournaments, bought boxes to run my own draft tournaments, bought boxes, bought cards. It was awesome, throughout the entire run, the balance of the different decks you could build, the versatility of the cards, the whole design was fantastic, and once the final expansion came out you could draft with some from each and MAN it was fun.
I'm going to say that I probably spent about £300-£400 on Magic that year.
Then came Time Spiral. Suddenly, it wasn't so hot to play with Ravnica. When Time Spiral was done, we had Lorwyn. I liked Lorwyn even less. The Lorwyn cards were just better, mana-cost wise, than all those Ravnica ones. As I said before, I like to spend money as an investment into the future. TFTD is still picked up and played through. Now I couldn't play with Ravnica any more - who would I play? Losing all the time's no fun.
This doesn't even cover the aspect of the game which is so competitive, that there are always going to be a couple of people who find the tournament winning decks and just buy those cards, skipping the 'do it yourself' part of deck building. What chance have you of beating their decks, without spending a corresponding fortune on more cards?
WotC announced they'd be increasing the number of sets released each year. That'd mean going through cards faster. I'd stopped playing by the point the cards had increased in price by a whopping 50% - a box of boosters for £85?! The game makes it mandatory to keep buying more cards! I'd already seen that all the cards I had particular fun with would never last, and so I lost interest.
Just before I do the short-form conclusion: as another example other than X-Com, I'll also add in a couple of other games for comparison. Twilight Imperium, 3rd edition: I bought this for £60, and the expansion for a further £35. This has given me many, many, *many* hours of enjoyment, with plenty of people, and bought around the same time. Another is Dominion: a card game, deck-building based, only it keeps everyone on an exactly level footing when it comes to building their decks. Only £35 for the main box, and a further £35 for the second one.
TL;DR version:
I used to play Magic. I stopped because it's ridiculously expensive. You have to keep buying more cards to stay competitive, and the number of cards released means a constant expenditure of a small fortune. Old cards do not age well. In the end, you're only buying useless bits of card. There are better, more cost-effective alternatives out there.