"Aces High" not "Medium Bombers High"?
Theres a lot more emphasis put on filling out the fighter planeset before the bomber set. We have a bare bones minimum of choices for bombers compared to fighters, but the game is also geared more toward fighter combat than strategic ops. Just look at the rediculous supply/factory network we have.
Plus, as many people will point out, the only thing the B-25 can offer over the B-26 is novelty. The Marauder is faster and more maneuverable. With the current emphasis on filling out the Northwest European planeset, there are many other aircraft that should, and hopefully will, be added befor the 25.
With the B-26, A-20, and Boston in the game, we will probably not see the B-25 added, if ever, until TOD moves to the Southwest Pacific Theater.