Every version of Civ Rev uses the same gameplay logic, so for each platform they have to do seperate art assets. The main versions were 360/PS3 and the DS art is simple. They didn't have the staff to do Wii art, or PSP art. If they do a Wii version, though, they probably will use that art or a variant of it for the PSP.
And honestly, there are no games like this for the PSP. Pirates is an awesome game but totally different. Meanwhile the DS has several (anno 1701, Age of Empires, Civ obviously). Do what I did, bite the bullet and get a DS.