Dave, I understand the point you'r making, but to me plug and play is a good thing. Also, when you say dcs is more complex... only slightly, from a technical standpoint. The two way communication is nice, but does not provide much more functionality in my opinion. As for running tmcc/legacy, that is not really anything special, the dcs system doesn't actually run any TMCC, it just sends out the codes lionel provided in the original book that came with the command base. I've done the same thing with a commodore 64 for fun, and routinely connect the tmcc base to a pc or ardunio for control. You can't pat dcs on the back for using information Lionel published in the manual, more than 20 years ago, especially when discussing what is not in the manual of DCS. Legacy/tmcc could just as easily be kluged to talk to dcs if the protocols were made public. Sending 3 bytes of data over a serial cable is not rocket science.
As for cost, I will agree that you get a little more bang for your buck initially with the TIU and AIU, however for technical minded folk, the fact that the codes are published means that one can build their own TMCC compatible switch and accessory controllers, My 16accessory/8switch controller cost about $30.
I don't really want to stray off into a measuring contest between systems. I have made my own judgements after polling the community here on what features each system offers and what problems each has, but for the most part both are just fine. when it comes down to it, however, the original point still stands, if you NEED to know something to make use of the system, it should be in the documentation that comes with the product.
JGL