There has been lots of upset amongst PC gamers that BF3 won't be on steam. This is because steam is very well established, they treat their users right and it's were all their friends are.
Instead of launching BF3 on steam they have created an equivalent to steam called "Origin". EA have said that they are in no way trying to compete with steam (which they obviously are as they have pulled it from steam and steam alone not they other download stores).
The reason I say not to worry though is because you can still play the game with your friends using origin and if you still aren't happy you can simply launch the game through steam so you keep your steam overlay.
Don't let the greed of EA ruin the chance to crush CoD and don't let EA ruin this for DICE. They are possibly the best developers ever (2nd maybe to Valve) and always produce excellent games.
PS. For those who don't know what steam is, it's a virtual store and community were you buy practically and PC game on the market and download it to your PC. The community part is a way of chatting and playing with your friends.