Agree with the sentiments above. Loved the episode, but was wondering why there were only really four examples were discussed (although several were mentioned as noted in OP) and all without a mention of mobile ones, and not even the mobile ones that got ported to PC (I'm thinking of you, Kingdom Rush). I know it is impossible to bring up all of the different TD games, but the platform does play a pretty big part in this particular genre, in my opinion, to not get mentioned. Tablets are just too perfect of a platform on which to play tower defense so at least a nod would have sufficed.
Glad spelk made a great list—would have done the same thing at midpoint of the episode if I hadn't been driving at the time.
All that being said, still a great episode! Really enjoy listening to these guys each week!