Valve is successfull enough to concentrate on what they want to do rather than the painfull buck earner...
Whatever game they do is a success anyways, so sony would have to pay big to force their hand.

THis does not exclude them comming to PS3 on their own.

(and they do linux too :p)

I doubt Sony will pump any money into Valve, for a number of reasons:
1. Valve's core market is PC (and now Mac) with Steam and the few (albeit very good quality) games they sporadically release.
2. The X360 conversations are just easy ports of the PC codebase, so an easy revenue stream, and I really don't think they are console system selling titles (most console owners also own a PC/Mac so would buy something like Half Life 2 Episode 3 for their computer as it would be clearly superior).
3. It's too late in the console generation to make any difference profit-wise to Sony whether Valve do PS3 games or not. If Valve decide themselves that there is a significant reason to tool up for PS3 they'll do it on their own.
4. The recent introduction of Mac versions of Valve games is to entice Mac users to use Steam and keep using it - and buy more games in the future as they appear. Steam would never be allowed on a Sony (or Microsoft) console, so that incentive to port current Valve games is not there.

Does anyone here know what kind of games valve make? is it mainly shooters??

HELL NO!

If Sony is going to pay someone it should be Square-Enix or ATLUS. Their 1st Party JRPGs are lacking so if they can't do it they should pull a Microsoft and buy the support

Sony has a lot of great development teams pumping out great games for there platform. Why would they pay Valve to release games that only PC gamers really like. If I was going to play any Valve game I would play it on a PC. The only Valve game I liked was Half Life 2 and I wouldn't dream of playing that game with a controller

i don't care valve anyway they should just stay on the 360.

I may be wrong, but I believe Valve said there is nothing wrong with developing a game on the ps3. People need to get it out of their heads that it is so difficult to develop for the ps3, developers now say it isn't. I would say it will be much harder to develop games for natal now. It will take up a whole entire core itself so is limited to only 2 cores for the game.

Even if they did, I will never care probably, I just can't imagine myself playing Valve games on consoles. Although, I am jealous of 360 owners bec they have splitscreen in L4D2 and probably in Portal 2 as well.

I never liked any Valve games. They games don't really need to come to the PS3 but the fanbase is growing close to 360 fanbase and could likely surpass it in the future so they are stupid to not make games for the PS3.