Previous statements from Google did say that 3.0 (Gingerbread) will be targetted at High End Phones while the Low End ones will stick to 2.1/2.2. And minimum requirements for the Gingerbread is 1Ghz processor. Currently, there is no guarantee on which current phone will get Gingerbread (Heck, some even waited like infinitely for FroYo) but those with lower than 1Ghz processor could pretty much forget about it for now.