Trying to focus on two different consoles will make things complicated and will make it harder to develop. Especially such a gap like PS3 and Wii? Think of the graphical, technical, and visual differences.
What happened to the GTA series after it came to the 360? People didn't like. Rockstar couldn't focus cause they had to do two different projects trying to make them perfectly the same, so they had to take some features out.
Proly the only company who did it well was the company who made CoD4.