In campaign, particularly the first few missions the tech tree is "streamlined" a bit.

I found this particularly frustrating. I started playing the game when it first came out and thought this had to be a bug so I stoped playing for a while hoping that a patch would fix it. I started playing again when I saw the 1.2 patch was out and since I still coun't research "trade" in the first mission I realized I must be doing something wrong and came here. If you look at the tech tree chart in the box you get when you buy the game you can see trade as a researchable skill. It would be nice if the game provided some sort of indication that its not avaliable for that level like maybe have it there and greyed out and not selectable. I mean if your gonig to go to the trouble of not letting me research trade you should remove the trade tab too so there is no confusion. Do the other levels remove other research braches I should be aware of?