Yes they can stop advertising it for playstation 3, But they cannot simply "Change" platforms, especially since Call of duty 4, 5 and MW2 already exist on the PS3 and already have a online base.
If activision were to Change platforms and exclude the ps3 well lets just say they would be re-funding over 100 Million people back, Why?
they cannot sell you a game, then ban you from the online services because of the console you are using, And if they did well then they would be facing a major lawsuit
so as it stands who gives a shit
black ops will be on ps3 and all the past call of dutys will stay on ps3 and the live option will remain
in the future if they want to make the newer call of dutys coming out a xbox360 exclusive be my damn guest. But for now they cant do anything about any of the past cods or black ops.
if they had their heads screwed on tight enough they would know that ditching the playstation 3 would cause them a TON of money lose. But if they want to skip over to MS then let them.. they can dig themself a grave!
hell i will give them the shovel, and if this pay to play shit goes through do you really think people are going to want to play their games anymore anyway?
um NO and then you have MS which is expensive anyway to have and run, and then u have the ps3 which is still free online i may add..
so after all this kicks in if it does, let's see which console sells more now