I'm from Brazil and I can say it happened before, as far as I remember N810 didn't last 6 months after they started selling it here. In fact, there were no updates to it's OS after it was launched. For N900, there was no great advertising, Ovi Store still don't have any paid apps, and I never saw it in any store (just online) so don't think it's going to be different, thought I really hope it will.
Anyway, community is still mantaining N800 and N810 OS, an update was launched recently. Maybe that will happen to N900 too, if all the devellopers don't buy the next phone and forget about the olders (see nitdroid for N8X0).