If anyone thinks that when their hard drive fails that magically their 2nd partition will be immune then more fool them. I honestly don't think that's the case at all.
Microsoft must think it's a good idea since their System Image uses a PARTITION on the same drive. Doesn't that lead users to think they are safely backed up?
I know some of my reasons to avoid using partitions were less than strong.. but when you add them all up you can't ignore the conclusion that a second hard drive is a far superior alternative to making partitions. Most of your arguments were basically "users would be foolish....." I just don't find that to be a solid selling point.