Going just from memory I can remember the talk about not seeing the same map (or was it mission?) twice in a play-through (I believe it was the pod-cast), but I can't remember that they have stated the number of maps in the pool. I can't recall any source saying the average missions being 25 for a play through. (What is the source on that tazong?)
Also, I don't think we can apply some pseudo-math on this. For example;
- If we take Jakes statement of "more than 2 and less then 10" mission types (let's use 7), and combine with
- 70 unique missions from the XCOM website.
- Then it would only take 10 maps to create 70 unique map/mission combinations.
And that just absurd taking into account we have seen 7 (8?) maps so far.
Reading the "70" source,
http://www.xcom.com/enemyunknown/info.php carefully, we can see that most of that is "marketing fluff", hazy descriptions & filler words. Made to sound cool, or just by someone not knowledgeable of the game.