not greedy, simply (business) rational.
they have invested for about 5 years in Maemo.org
now they have moved on and have closed the case.
remains to be seen for how long they will still support Maemo.org; possibly an open question, depending on how the community continues supporting "dumb" 770, N8x0 and N900 users and thus providing NOKIA a service (indirectly)?
but they don't want to have an OSS Maemo 5.5 / 2011.x competing with their new development & thus spreading dev ressources, maybe?

why
well, like you concluded too, there is a lesson to be learned from the Maemo.org business case; NOKIA learned it and decided that it was easier to make a new start then to try to fix it.
can't blame them on that, now, can you?


can't comment on that per se, think it was before "my time"
i finally bought my 1st N900/MID barely a year ago, even after NOKIA had already left it
but maybe you weren't the only who "hold back" because of the "" atmosphere"" (or whatever you want to call it...)
maybe stskeeps felt the same & agreed with NOKIA that it was easier / more effective to make a new start then trying to fix "old stuff" (no offence)?

EDIT: if you think of it, what NOKIA is doing is that not much different from what RedHat is doing.
support the OSS community (sort of, @ least with devices & apparently some infrastructure @ MeeGo (?)) but then using that for a devices they sell, with parts of code which are #NOT# open-source.
RH wouldn't be able to sell many server boxes if companies could get exactly the same stuff from CentOS (or Oracle w/ unbreakable Linux)
actually Oracle is becoming a problem (they have the money to replace the parts RH doesn't want to share & compete on the same market, (database) server market)
thus RH tried to tighten their grip on "their code"
maybe, NOKIA is getting dead serious about MeeGo devices?