[rsynnott]

> Actually there is no good reason Microsoft didn't write an X86 virtual machine so that their tablets could run the old programs.

There is. You'd be looking at something very much like Apple Rosetta. Now, the first Intel Macs were substantially faster than the PPC Macs that most people had at the time, but even then Rosetta felt painful. All current and near-future ARM chips will be slower than most current Intel chips; you'd expect it to be even more painful. Worse, for lightweight apps it would involve far more CPU usage, which would hurt battery life. People wouldn't _care_ that their Windows 8 tablet was getting two hours battery life while their friend's iPad was getting 10 because they were running a legacy app which was hogging the processor doing instruction translation; they'd just blame Microsoft.

The case of Java is a little different; both Dalvik and JVM are designed to be JIT compiled relatively efficiently to multiple common architectures. Architectures like x86 and PPC are generally _not_, and things like Rosetta suffer as a result.