Does anybody buy them at that price or is it just a case of Amazon vendors bumping prices due to it looking rare and spiralling out of control (with no or few actual sales ?)
I think that's the actual price. Other numbers of that book aren't going for nearly those prices, so it's not just a book being rare. Also, it's not just Amazon.
Frankly I think that Conway could make some nice money by making older editions available in electronic formats.