"If something could crash XP, it should be able to crash W7 transparently through VXP"
Pretty sure users are going to be willing to give up a degree of entanglement to both be able to run their XP apps and have a system that doesn't crash. That alone would be an incentive to upgrade to W7.
Classic on OS X worked the same way, too: a Classic app could take down the entire Classic environment, but OS X would safely charge on apace. This was definitely something that helped drive people to upgrade.
Pretty sure users are going to be willing to give up a degree of entanglement to both be able to run their XP apps and have a system that doesn't crash. That alone would be an incentive to upgrade to W7.
Classic on OS X worked the same way, too: a Classic app could take down the entire Classic environment, but OS X would safely charge on apace. This was definitely something that helped drive people to upgrade.