Nova and Avanquest are both contracted through Parallels to sell their product, you might be taken to one site or the other when you go to place an order. Here is a chat i had with "Scott" with Nova in regard to upgrades and buying the discounted version available on sites like amazon. Hope it is useful.
Chat Content:
Scott: [12:43:46 PM] Welcome to our real-time support chat. How can I help you today?
Carl: [12:43:52 PM] Hi
[12:44:07 PM] I already have P5 and I got the upgrade email about 6 for $49
[12:44:40 PM] But why would I do that if I can go to Amazon and pay 49 and get a 20 rebate back from you and then get a free upgrade to 6?
Scott: [12:46:23 PM] That sounds like a lot of work, but I couldn't beat that price for you. Please be aware the Parallels rebate is one per household, so it won't work if you've already received a rebate for your previous Parallels 5 purchase.
Carl: [12:47:34 PM] Don;t think I have, I purchased online a while back, seems many are going to do this in the forums, why not just sell the upgrade to "loyal" Parallels clients for $29?
[12:48:10 PM] Seems like every year we have to upgrade at a substantial cost, doesn't seem fare to me
Scott: [12:48:31 PM] I understand your concern, we are contracted with Parallels to sell the product at the price they've set. Please note, however, the upgrade is not mandatory if you don't want the expense.
Carl: [12:49:00 PM] I see, ok I will take that up with them then, thank you for your time.