It appears this will not always be the case however, with this response to a question asked on their support forums:
Is TweetDeck available for mobile?
TweetDeck is currently available for the iPhone. You can download it from the AppStore or go here http://tweetdeck.com/iphone/
We are determined to eventually see TweetDeck available for other mobile platforms, such as Windows Mobile, Symbian, Blackberry and Android, but there are no timelines for these as yet.
Hopefully the company will bring their software sooner rather than later, or risk being overtaking by the many other Windows Mobile clients like Twikini, which is just getting better and better.