i believe there was a promise once (after the 770-fiasco) that tablets would be supported for at least 2 OS-releases each. i tried to search both google and talk for the exact source but was unable to find it (hard to find search terms that dont generate too much unrelated noise). still i'm pretty sure i remember this correctly as it was repeated several times with regard to N800-users (along the lines of: they'd benefit from N810-upgrades as the N810 would see 2 more OS releases which of course would run on the N800, too.)

also, iirc, the explanation for not keeping this promise was that they counted each diablo-SSU as an OS-release... well...