forcing software to run under a virtual machine adds one more layer, so no matter how good software can be designed, compared to similarly optimized native software it will always mean more code to be executed, that is, more time needed to execute it and more space needed to contain it.

They used the VM approach for security reasons, which to me is terribly wrong. Mobile terminals should have hardware separation between subsystems, that is, the sensitive stuff (radio) enclosed in black hardware boxes where data goes in and comes out, just to make telcos happy, but everything else -I mean all the OS and apps- should be native and user accessible. This way one gets the best possible performance while maintaining a high degree of separation between kernel+userland and radio chipset which would let allow hacking whilst preventing anyone to tamper with cell connectivity.