[quote name='exileinoblivion']I just got a gaming laptop in the mail and I'm completely new to pc gaming. Why does everyone love steam so much?[/QUOTE]
For me, it's just become the face of PC gaming. It's an extremely well built and well organized system that manages all of your games (and your settings if the game supports steam clouds). In addition, they did a good job of weaving in the community aspect so much like XBox Live (and probably PSN. wouldn't know since i never really game on there) you're always connected to your friends and regular gaming groups all from one interface.
One major thing is that as said above, Steam always has -excellent- sales. Typically three or more a year, where you can get games for stupidly cheap. (Super Meat Boy for $3.75 as one example, from the last Christmas sale)
You also don't have to worry about DRM really. A number of games still retain some but for the most part, Steam games come with no additional DRM aside from just having to log into Steam itself. I've seen plenty of games that had limited activations or the like, only to have them removed from a Steam version since the service already does a fairly good job (as good a job as anything else) on rights management.
Oh, and apparently the EULA is written such that if the Steam service ever goes down, we get full copies of our game that we can install as we wish. Point being, unlike services such as XBL or PSN, there's no need to worry about losing your games if the service ever goes down for good.
So yeah. Great interface for purchasing, managing games, as well as community hijinks and less DRM for the most part, plus the promise of still keeping my games should the service fail. For me, that's why Steam is so amazing.
[quote name='exileinoblivion']I'm sorry, I should have specified more. Why is everyone worried about whether you can register these on steam or not?[/QUOTE]
And to answer the question that magically appeared whilst typing my wall o' text, as already said above. It's nice to have all of your games kept together. (Though if you're paranoid about digital copies lasting, the whole EULA thing listed above doesn't hurt either)