The whole story just sounded so contrived from the start and didn't play out much better.
I mean, we know 37signals and reality are not best friends, but just throwing away 220k/yr in nearly passive income if it doesn't sell for the desired price, seemed a little far out there to begin with...
With that kind of money at stake I'd have expected at least a little more enthusiasm in the flippa-auction from their end. No least given how much DHH likes to bash the VC-gambling - how does that jive with playing russian roulette on a product raking in that kind of money, for no plausible reason?
My pet theory is similar to yours; I think they simply had a buyer from the start, and offered to throw in some "37signals original flavor media spin" as a bonus.
Whichever the truth is, it obviously worked out for them.