* Chastises them for making free apps in the past
* Reminds them they've had to distribute their apps for free (almost as if they should be grateful and now give them some money)
* States they would accept their app if it provided unrelated functionality or access to competitor products (who are oddly not subject to the same rules).
* Implies that everyone is following the rules but them (which is demonstrably false even if you accept the "Reader" and "Business" definitions they provide)
Also, according to DHH, they leaked this letter to the press before sending it to the Basecamp CEO. Nice.
The argument is so strange, it's almost as if "email" is a special term of art that causes Apple to categorize this app in a way that is not is not consistent with other SaaS products. Even with that said, there are no other similar email apps like Superhuman that are subject to these rules. If I was a Chat or Email based SaaS company CEO and I relied on the iPhone to complete my multi-platform value prop, I would be very worried about this happening to my already approved app.