In this sense it was not significant upgrade at all. Yes CPU is a bit faster and there is more RAM but nothing significantly different. You cannot compare it with big changes in architecture like going from 32 to 64 bits. It is like going from PC with 64MB RAM and Pentium@266Mhz to PC with 128MB RAM and Pentium II @333Mhz. Such changes happen all the time and there is no technical excuse for not having OS2007 running fully on N770. In fact this is what hacker edition is and you can see that it works quite fine on N770. The reasons for ditching N770 were not technical. They simply had no resources for maintaining both devices.