The big draw for the VT is the ability to import your characters from the Character Builder and have the macros required to use the powers already programmed. In addition, as mentioned, monsters can be imported automatically from the AT and have their attacks built in already. No macro programming knowledge is required. Finally, subscribers to DDI also have a number of character slots (I want to say 50, but I may be wrong) on the VT itself (separate from the Character Builder VT slots) that can be used for tracking characters over the course of a campaign played on the VT.
Now, whether that is worth a monthly subscription fee or not is a different question. One that is personal to each person.
I concur, though I am still disappointed in the promised/delivered ratio of DDI. The 3d VTT was the main reason I gave 4e a shot when it came out, and the overpromise/underdeliver aspect of the DDI was just one of the many reason that edition didn't get played for long at our table.
Still, given this history, I would prefer to go with a product that has been tested, used and de-bugged, though I can see that the DDI integration is a very attractive feature if you're a 4e player. I still pine for that 3d VTT, though. Sigh.