I personally am not surprised by this and it all fits together like a snugly-fitting puzzle. Microsoft has migrated away from supporting stand-alone devices like the Dell Axim. Windows Mobile 6 clearly demonstrates this in that it is specifically coded for phone-based devices. I'm sure that Microsoft advised all the OEMs a long time ago about that (so that they could develop the appropriate hardware to mate with the OS if they wanted).
Dell has never been interested in doing a phone-based device, so the decision to shut down the Axim line was a sealed and determined fate the moment Microsoft decided to develop exclusively for phone-based devices.
Of course, even though it makes sense, it is no less of a disappointment.

I've always thought that the merging of the phone with the PDA (and the mini-laptop it had evolved into) to be a compromise I wasn't willing to make. I never want to be tied to a particular cell network because of the PDA I use; if I want to quit the contract, I have to buy another device? Yuck! I'd rather wear 2 devices to divorce those 2 conflicting interests from one another.
All the same, thank you for the confirmation of our suspicions!