I'm going to give my perspective, since I've been a casual PC gamer for years, but recently bought a PS3. Before the PS3, my last console was an Atari 2600 (never had a Nintendo, Genesis, anything else).
I primarily bought a PS3 because my brother and I wanted to do some gaming online, and he already had one (bought for the blu-ray player). After playing with the PS3 for about a month now, I have to say that I'm really impressed with it. It's very easy for my brother and I to get online and have some Co-Op fun in RB6-V2. The bluetooth connection is awesome for chatting, and everything works very smoothly. I'm also impressed with the level "home entertainment" options built into the system, and what the Playstation store offers for downloadable games (I know it doesn't compare to XBox Live, but that's another discussion). Also, I gave up on NCAA football ever being released on the PC.
My brother and I tried some gaming online with our computers, but there were always issues. Either with the game settings, router settings, drivers, even just getting on the same team was problematic. It was just a pain. It's not that I don't know how to game online with a computer, I was a regular member on a squadron for IL-2 for a while, but trying to get someone who isn't as computer-savy to understand things like port-forwarding is trying.
For me, the hey-day of computer games were the fun flight and space seems, that got you personally involved in the action. Games like Aces of the Pacific, Wing Commander, X-wing series, Freespace, etc. (stuff you need to play with a joystick). However, the flight/space sim development has been on life support for a while. IL-2 while fun, was also getting a little too complex for me to want to put time in (I don't want to worry about varying engine mixture or prop angle), and it was a little sterile, the game never put you into character. Don't get me started on the complexity of Falcon 4.0.
The fact of the matter is, while I'll still get games on the PC, my primary gaming platform is now going to be the PS3. It's nice being able to just pop in a game, and play it from my recliner on a 46" screen. I don't have to worry about upgrading hardware, updating drivers, figuring out conflicts, etc. As I've gotten older, I just don't want to spend my time doing that stuff in order to play a game. Now imagine what those people go through who buy store-bought PCs with integrated graphics etc. I'm not afraid to admit that I'm a casual gamer, I just want to play and the PS3 allows me to do that easily, even with my brother in another state. If fun flight/space sims come back for the PC, I'd be all over it, but I don't think that's going to happen because there's little to no money in it.
There's my 2 cents.