Blame Twitter not Tap Bots. Twitter's new rules limited the number of user tokens that third-party Twitter apps can use so if they had priced it at what they originally intended (which probably was somewhere between $5-$7) they had no chance of making money on this app. By pricing it at $20 they have that chance with the limited number of user tokens they are allowed to use. Expect to see the price go up on other third-party Twitter clients for the same reason. It's ridiculous.
TweetDeck, which is now the official Twitter client, is greatly improved with its latest release, and is free. I would have no qualms using it as my primary Twitter client if there was a way to sync reading position but as far as I can tell there's no way to do that with Tweetmarker, iCloud, or anything else. This is a dealbreaker for me unless I'm missing something?
So either I'm going to go back to the free version of Twitterrific or pony up $20 for Tweetbot.
-PN