Apparently the 505 has some different hardware arrangements internally too. The most obvious is the USB Mass Storage capability that the 505 has and the 500 doesn't, though I rather doubt that particular one is an issue here.
More likely factors are the difference in memory they have to work with in the 505 vs. the 500, and I believe that the 505's processor is a step up from the 500 (could easily be wrong on that one, I don't clearly remember the details
). Either of those could put whatever they're doing to reflow (and we haven't the foggiest notion what that is, as of yet) within the 505's capabilities, but outside the 500's.
Then there could be other less obvious factors that mean the 500 couldn't handle this function.
I
don't know that it can't, by the way, and I really hope that it
can, personally.
So far as I know, the Sony view on this point is
still that they'll update the 500 with new features as they can, but they aren't promising to do so, citing concerns about potential hardware constraints.