. . who just wants his machine working the way it did before, redeployment isn't generally an option.

In some cases, particularly with Windows XP, I think the blue screen is due to previous damage by worms and trojans. They may all be cleaned out and the machine may be working just fine, but there still may be damage to system files which causes failure during update. The failure cases I've had have been when updating after cleaning out serious infections, but that's about the only time I update a Windows machine. Sometimes it seems cleaning out infectons is about all I do these days.