
Originally Posted by
2K Greg
I asked the devs about this and got an answer for you.
The higher difficulties give fewer goodies (and of lower quality,) as most of you probably already know. Also, as has been hypothesized above, only certain techs are available through huts, and a unit can only get one upgrade via huts.
The final thing to note is that there is code that keeps you from getting the same reward for a while. So while it's not diminishing returns per se, it may feel like that if you happen to get a couple great huts in a row.