FYI, this is because of HG's affiliate program. So make sure you cleare your browser cookies (at least the ones from hostgator) before you visit the
Hosts page , then click on a host and make the purchase, you can make sure you have the affiliate cookie in your browser cookies (cookie name = __utmz | content = ##################.utmcsr=
appthemes.com|utmccn=(referral)|utmcmd=referral|utmcct=/resources/wordpress-hosting/ ) and then proceed with purchase. Then send in the proof of purchase and you should be fine. (BTW this is against the TOU in the HG affiliate agreement , FYI ;) ) Make sure you do not buy later, after visiting other sites since cookie might change and do the purchase with the same browser (don't switch between IE FX GC etc.... )
Happy shopping! ;)