Twitter: Want unlimited API calls?
TweetDeck: YES!
Twitter: Okay, thats $XX,XXX a year...http://socialmediatoday.com/imckeevocaniccom/282916/how-many...
http://groups.google.com/group/twitter-development-talk/brow...
It seems stronger than merely a "recommendation" to me. They flatly state that new apps may not replicate the mainstream Twitter experience. Existing developers are allowed to continue to "serve their customers" - but I think developing new product lines as TweetDeck is doing, is going to run afoul of the new API terms of service.
Unless they have a side agreement, I expect some sort of battle to arise from this.
Though there is always the chance that twitter tries to buy tweetdeck.
Twitter's now-infamous developer group post also listed a number of areas Twitter doesn't want to own. Reading between the lines, they're giving client companies the opportunity to transition to another line of business. If the client companies don't take the hint, Twitter's going to eventually play hardball.
Don't think they'll give it up that easily