[comex]

The difference, as it pertains to the patent issue, is nothing technical - it's simply that Intel feels threatened by Microsoft's emulator and not by qemu. (Though if Intel has ever redistributed qemu, there may be an additional GPL wrinkle...)

[rwmj]

Intel contributes to qemu (or at least, developers with @intel.com email addresses contribute). However AFAIK they don't contribute to the emulation code (TCG).