You guys are hilarious. The vast majority of people who buy something like the mac pro are most likely not concerned with its aesthetic appeal. To a degree people like to purchase something familiar to them that fits their needs. If they've migrated to likely hardware, they're less likely to pay the additional expense to go back without a guaranteed advantage. I don't see it happening. I've seen so many people with painfully slow computers (not just by computer model, but actual performance of their machine using installed applications) yet they don't seem to notice what is wrong. If they migrate to something like an imac or mini, they're unlikely to go back. They're also unlikely to replace it much faster unless they're facing internal component failure. It's just not the kind of market that favors trendy products.
Edit: I meant people who migrated from an earlier mac pro or G5 tower to a newer mini or imac.