Yes, the video does enlarge when watching QVC live through the app on the iPad. I've just tested it. Turned the iPad 90 degrees, which enlarged the video and then tapped the little arrow button in the top right hand part of the screen. It then further enlarged although I can now only view 3/4 of the product detail box. But it does do it. I've just tapped the arrow box again to reduce it to the normal enlarged size and I can see the whole of the product info box now. The streaming is super clear though.
Return the Prestigio, you know you really want an iPad!
On a serious note, why don't you pop into a store to look at an iPad. My local Tesco has one on display. John Lewis is another store that has them on display. if you live near an Apple Store you could also try one out there. I think if you buy direct from Apple and aren't happy with the iPad you can return it within either 14 or 30 days for a full refund. Apple are extremely good at customer service, and particularly after-sales service, unlike many tech companies.