I don't want to disappoint you, but you won't get significantly better Web App 1.0 support (AJAX etc.) nor will you ever get Flash 9 on the 770 (I'm not even sure the 770 has the CPU/memory to play Flash videos acceptably).
Nokia could go bankrupt tomorrow yet the 770 will continue to receive application software updates - the 770 is not dependent on Nokia, except for firmware updates.
Want the latest version of Windows Mobile - guess what you do? That's right, buy a new device! Although some manufacturers may offer chargeable upgrades of the latest OS for existing devices, this is the exception than the rule.
Oh, and the 770 is nothing like a 350Mhz (Pentium II?) with 256MB RAM!