Perhaps, they (whoever is Formdworks) didn't have the time or the knowledge to make the payment gateway work this way. Just consider the possibility for them to have some limitations. Or maybe it was a simple and accurate way to make the numbers.
If were him, I would do the same to prevent "too hyped and optimist customers" from ordering more than one. You know, people are hyped as f...k these days. We are all really excited about the idea of buying one. So, you make a call to friends, wife, brother in law, uncle, the dog, the hamster and pre-order 5!!
Three months later, "Do you remember my hamster? So bad it passed away... And my wife? Dude, I broke up... She cheated with my brother... Now I'm broke because of the lawyers...". All of a sudden Formdworks has to deal with an undesirable and expensive stock. If you have to lock 1000$, you don't feel like that wonderful and nice guy anymore... And Formdworks save some money on the way.
Refunds and cancellations hit hard on anybody's business plan. Given this is a pet project not backed by any Kickstarter, seems reasonable to play safe.
That's the movie in my head! 
But I could be wrong!
