I think sometime during the "explosion" of offerings started in the late 90's (remember the 3 catalogs per year craziness? Or 6 for MTH since they did one for Premier and one for Railking back then), at some point each manufacturer left a few things off of their potential offerings realizing the other had a firm foothold.
Just my guess there. Examples: While both Lionel and MTH did Shays, only MTH did the Climax and only Lionel did the Heisler. Two very unique mechanical designs that I would have to assume involved a lot of $$ to do the engineering to produce each. Also, MTH definitely had the (mostly) cornered market on the subway set realm (and since Legacy did not include any functionality similar to MTH's Auto Mode for these, that would be a hard thing to compete with, even with the cool commandable opening doors 
). True Lionel did 3 subway sets, but they were very similar (if not identical) except for very small details (possibly the window shape on the end doors?). For the most part the difference was the paint job. Other than those 3 offerings, Lionel stayed away from that market. Also the Triplex. I'm sure the engineering to get that right was a bear. MTH expended the effort, so it made sense for them to offer it a few times. How much of a market is there for those that Lionel would also sell enough of them to make it worth it to put in the R&D $$ to pay for itself?
So my point is with MTH stepping out of the picture (unless something miraculous happens), possibly Lionel may look at such things differently in the future with no other large competitor to worry about.
-Dave
