I believe you can use a mouse/keyboard on the PS3 so porting RTSs to that console shouldn't be too much of an issue. The real problem comes from the stigma surrounding the genre on consoles. If people aren't going to buy it, the publishers aren't going to sell it.
As far as the 360 is concerned, I remember hearing a while back that MS had some back room deals with PC companies saying that they wouldn't get involved in PC development and that MS consoles have avoided using mouse/keyboards so that they don't infringe on that deal. I don't know how true that is but I can see it happening.
but there is red alert 3 for the PS3 and is joypad only, as I said the only game to use m/k method on the ps3 is UT: 3. I don't think its anything to do with stigma, I don't think developers can be bothered