How to get paying customers before you start writing code (blog.reemer.com)

One question on this- how many of the committed buyers actually pay, or at least subscribe for a minimum period of time?

I could imagine a significant # committing and then pulling out later on. I'd like to see some stats on that as a conversion rate.

Getting customers is not tough if you have a solid idea that sells, This article was worth a read, Helpful enough. But should we all expect our customers to pay first before writing a code? I think that's not always possible.