The Lurker has posted two LENGTHY threads on upgrades- entitled "A word about upgrades" parts I and II.
The bottom line, if there is one, is this:
A hotel will upgrade you to what they see fit. The terms and conditions are that flexible. There are some hotels where no suite is exempt from the upgradeable list.
There are other hotels where noone has ever reported getting a suite, and it seems as if all (or virtually all) suites are exempt from upgrades.
It stinks for us, since nowhere is it published how many upgradeable suites each hotel has. You just need to compile that information on your own and figure out which hotels are great about recognizing elite status, and which ones are not. It's be great if Starwood told us instead of us flying blind.