First, I really can't imagine buying a game like this on a console.
Second, I really can't imagine EA only bringing Will Wright's next mega "Sims"type game to a few consoles. I wouldn't be surprised if they shoehorn it onto cell phones in the near future.
Third, just because EA decides to take it to only 2 consoles and one is the 360 does not automatically mean the PS3 is the other console. It has in the past but that is due I think to a simple business calculation that changes everyday and with every game (that is of course aside from many of the games being developed prior to Nov06 when the PS3 and Wii positions were expected to be the reverse of today). Simply put, when deciding which 2 systems, at the moment and probably always one will be the 360, the 3rd party has to decide if the cost incurred by porting the game from the first system can be made up by the expanded sales offered by the second system. For most games so far the PS3 offered, or was thought to offer, a better return.
For example, take a hard core FPS for the US market. Porting to the PS3 adds 20% to the cost, to the Wii 40%. However, in the US the PS3 has about 33% the install base and will buy this game as much as the 360 user base so 20% more cost for 33% more revenue is a good deal. The Wii has a user base about 66% as large as the 360 but say either half own a 360 (not an issue with the PS3) or don't buy FPS' then the Wii only offers 33% more sales. In this case 40% more cost for 33% more revenue doesn't make sense.
Now lets look at Spore. I think this is more of a NA/EU game so I'll use those markets. For the PS3 the game again would add 20% to cost but the PS3 may not be as fertile ground for a game like this so it would add some amount less than the 30% it normally would. Whatever lower amount it would be dangerously close to 20% making it not worthwhile. A Wii version would cost 40% more but the Wii would add almost 70% more potential sales (in this case I'm assuming Wii60 owners are balanced by the game being more popular with the Wii install base). That's a much better deal than the PS3 in this case.
Of course it's more complicated than that when actual costs and potential sales are used but I'll leave it at that since it's long enough already and it basically explains why a game could come to only the 360 and Wii even if many haven't so far.