This is a good summary of our confusion. :) Sorry to be a pain about it. Would you agree that I can "purchase" the contents of a suitcase on a gameshow without knowing what they are? Or that I can "purchase" next year's wheat crop from a farm without knowing how large it will be? Or I can "purchase" 100 shares of Facebook stock to be delivered in a year? I think most people would. And this is true even if it turns out that the suitcase is empty, or the wheat crop is a bust, or the stock is worthless -- it's not that I haven't purchased anything, it's that I have purchased nothing.
But the point isn't really the word. The point is that if you're offering a valuable reward on Kickstarter, some backers will think of it as a plain old financial transaction, where they put some money down and they get to have one of whatever you're trying to produce if you succeed. And that's totally fine as far as Kickstarter is concerned. So if it's not how you want people to think of your Kickstarter project, you have to be careful how you position it.
But the point isn't really the word. The point is that if you're offering a valuable reward on Kickstarter, some backers will think of it as a plain old financial transaction, where they put some money down and they get to have one of whatever you're trying to produce if you succeed. And that's totally fine as far as Kickstarter is concerned. So if it's not how you want people to think of your Kickstarter project, you have to be careful how you position it.