I'm assuming that as long as I purchase from an authorized dealer, I'll have access to the software updates that will enable this on the TX-1000, or would it be wise to delay my purchase until this is confirmed?

According to Eric Johnson, VP of Technology Universal Remote Control, Inc:

Post 11 made on Friday June 30, 2006 at 13:54
"Eventually, Device+/- AND variables will be added to the MX-900 and the TX-1000."

"Now, since I've let the cat out of the bag on variables etc., let me just say, please be patient. We have a limited amount of resources and these features take time to test before release. The use of variables in particular requires a substantial revision to the software, which will take a few months. However, it IS coming."

[Link: mine.remotecentral.com]

Eric seemed fairly confident that URC would roll this out, I hope this has not changed.

Thanks Again