Architengi;
You are speaking of Symbian S60 from your perspective with the Nokia N95-8GB correct? You are missing a bit...

...the OS there is older than what's in the iPhone (all versions)
...user data preservation is in Symbian S60 v3.2 and v5 which are both the current versions of the OS
...OSes should not guarantee backward compatibility unless you want Windows-like experiences with every device (high memory usage, legacy user interface conventions, etc.). Developers who are only coding for v3.1 of Symbian are way behind the times; and those coding just for v3.2 are not working with the best iteration of the OS either.

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Maemo isn't the normal Nokia OS/developer story. Besides using different methods to interact with the developer and user communities, Maemo has allowed Nokia to move away from some of the antiquated coding methods that has made for quickly obselete OSes (one of the benefits of open source and agile-based software development).

That being said, Maemo 5 applications will not be comaptible with Maemo 4 unless the developer makes a different version for the older OS. Progress - in this respect - means that older devices will get left behind. This doesn't mean that Nokia should stop selling older devices. These older devices are not only mature (in terms of software and hardware), but they also offer a lower cost to entry for those looking to get something solid, but not pay the "early adopter tax."

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Your issues with Symbian should be taken up with the Symbian Foundation. S60 is now their baby. And for all that you've nicely stated in the timeline, S60 v5 (^1) is pretty much a solo effort by all licensees. It will be S60 v5^3 that does the most towards making Symbian a malleable platform - ironically, just as much as Maemo 4/5 is now.

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It is not the manufactuer's responsbility to make sure that you can upgrade to anything. The device and associated software you purchase as the intended service you'd use. They make no guarantees towards future use or even updates. To expect otherwise is to be a more immature consumer than those who just follow the latest trends and call themselves advanced.