I think they do want the paid upgrade however I've gotten free updates to a great program since 2009. I have to agree that they have built an awesome tool that is incredibly easy to use.
Their thinking is made clear in this quote, they don't see the lifetime license as a viable business model.
"However, considering that we need to be able to feed our families, it is likely that 1Password 5 will be sold as a separate paid app, like we did for 1Password 4 in the iOS App Store. We just decided to make 1Password 4 for Mac an exception to this."
http://discussions.agilebits.com/discussion/16268/what-shoul...
They are referring to AgileBits customers on the Mac App Store. So anyone who previously purchased 1Password on the Mac App Store. Apple doesn't offer upgrade pricing, so it would make sense that the upgrade is free. Most likely AgileBits calls that fact out due to past issues with the iOS App Store where they took down the old app and created a new one so they could charge an upgrade fee.
I like the approach that http://airpair.com took, they let the mentors choose their desired rate. They also let the students choose from a list of qualified applicants.