The idea behind selling the source code is educational. There aren't many resources out there for folks who who've never built a web app before and want to see a complete one for reference.
As for Gumroad, it will go up for sale there soon, but the publicly available price will be 4x the winning bid amount, so if you want it, you're best off bidding. :)
"There aren't many resources out there for folks who who've never built a web app before and want to see a complete one for reference"
As there are completed web applications that people can look through.
Not many previously closed source, fully-commercial SaaS web apps have been completely open-sourced. If you'd like to debate what "not many" means, I suppose we could, but I think that's missing the point. I, for one, can't think of any.
When most startups shut down, they take all of their code with them. I'm kind of surprised that anyone's response to doing something to changing that status quo would be negative. I mean, I'm sure you'd like to have us just give it away for free, but why? Why would we do that?