Perhaps it's because it is a hard show to film?
When people see $200 HD camcorders available (that are very portable) in the the store, it makes it harder to accept this reasoning.
Too many people out there can ask themselves, "I could film Amazing Race in HD with equipment that I personally own -- why can't CBS? After 14 seasons, they should have been able to save up enough to buy some HD handcams." Sony would likely give them a deal on 10.
Of course, it likely comes back to the "TV stations can't use consumer-grade equipment" issue, although I'd prefer consumer grade HD over professional grade 4:3 SD.
I'm not sure I can watch another season if it is not HD, or at least widescreen SD.
Someone on the Amazing Race team should watch an episode of Survivor. I think HD has definately given that show a boost -- it is some of the nicest looking HD on network TV.
Amazing Race could be an HD program fairly easily. Static setups like the interviews, mat chats, detours, speed bumps, etc could easily be handled with single HD cameras. Then just insert SD widescreen for the field shots and helmet mounts and things.
The only reason I can see that they don't do this is that they can't be bothered. The show is broadcasted in HD so there is no reason why at least some of it couldn't actually be HD.
EDIT: While there are $200 HD camcorders available, you would likely want to spend $1000 and get one of the hard drive ones, along with some spare memory cards. But even $1500 per set should be affordable for CBS, being a big media conglomerate and all.