[quote name='dyeknom']constipation is the leading cause of backlogs.[/QUOTE]
That's when I get most of my gaming done.
Edit: Caught up with the thread. I grew up pretty poor, and I had Sim City 2000, Doom 1/2, StarCraft/BroodWars and almost nothing else from 13-18. In college, I started pirating a lot (and borrowed a few games), because I was still poor. I never had a console growing up either. And my family had one TV. I always had the intention to buy games when I started making money. So fast forward to a few years ago, when I started having disposable income. Now I have a big library, with 1 single sports game (FIFA World Cup, from GameFly's year-end sale). So it's my way of catching up, but of course, with the disposable income comes less time. So yes, a big part of it is that I'm buying because I never had them.
Also, I don't buy them to profit, but it is nice to say, yea, I have a sealed copy of Infinite Space, or some other game I find are underrated. It's not like I go out and buy Modern Warfare etc either, since I have 0 of them. Most of my collection is RPG/SRPG, which like someone else said, causes a bigger backlog due to their length.
And about the hobby games... I'll admit that I spent a lot more money than I should have playing Tekken Tag/4 at arcades. I estimated about $10k spent on those in 5~6 years, because it was almost all I played from 2000-2005. Almost all the money I made while working in college (and then some) went to that. I don't really regret it, because it's pretty much the only competitive game I didn't get bored with after a few months. I played Counter Strike for a few years, and I was the one using scouts and pistols. And still ending up on the top of the list in most games. I wasn't that good, but most people just sucked. I played FFXI for several years, and our Linkshell accomplished some pretty nice stuff, like supposedly the first North American Linkshell to kill Tiamat. I do wish I was that competitive still, a lot of times. I try to get my GF to play Tekken and other fighting games, but she won't, because she says I cheat =P
tl;dr: I see it as a library, I'm making up for not having games when I was young.