So without actually playing them, how do you know that the PS3 sequels are not gonna be different?

And if they arent that different its because they know what sells.
Look at MGS & GT for instance.
Both have not changed the formula in huge ways (although as with anything, tweaks have been made along the way), yet both franchises maintain a huge fanbase, and constantly top sales charts whenever a new version is released!

Sometimes it doesnt pay to fuck with what works!

You can bet your bottom dollar that most people will buy a PS3 purely on the basis of these games!

The formula of change hardly worked for the Gamecube now did it!