It's as simple to commit projects to github as it is to sf, bitbucket, google code, etc. Wait... you need to set up ssh credentials on github... sorry, it's more difficult to commit a project to github than it is to most of the alternatives.
>Also love the idea of a centralized place to follow all your favorite projects.
It's good that we like different things. I love the FACT that there can't be such place, it's technically not possible, fortunately!
>If linux can be on github i would think php could as well.
Linux is not on github, Linus Torvalds has one of his branches of the linux kernel on github, doesn't mean that he doesn't push his commits to other places too, which he certainly does. Also, linux is much more than the kernel, and its bits are hosted in literally thousands of different places. Finally, you can maintain your branch of the linux kernel wherever you wish, there's no mystical force forcing everybody to use Linus', you can use whatever kernel build you want from whatever sources you want. So saying "linux is on github" is a rather vague sentence.
Don't get me wrong, I like github, I would hate not having a reason to. It appears to me that most of the people don't relaly know why they like github. Because it's popular maybe?