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The thing is, most people don't see ARM based computers as "computers".
I can still talk to wifi devices. I can still use bluetooth. I can still make GSM calls. Maemo binary blobs won't stop working because some new update in the core software causes an incompatibility.
With the N9 coming out, development will shift to it, and away from the N900. That means fewer people working on the N900, which means fewer people fixing and tweaking (or caring about) the N900.
By whom? Nokia has never promised it. MeeGo has never promised it. MeeGo CE has never promised that MeeGo would ever be "productised" or ready for the average N900 user.
Tell me: When the N900 was announced, how much work happened on Diablo on Nokias part after that date?