From the apple specs, the 15" has 1066 memory while the 17" has 1333mhz memory, but I doubt there are any significant technical difference between the two models and think that it's just a gimmick to try justify their ridiculous profit margins.
Either way, 1066 memory is not significantly cheaper than 1333 one, and if it doesn't support 1333 it'll just run at 1066 by default, it won't hurt anything if you put 1333mhz sticks in it.