In Wings of Liberty, the mission order can be changed and it matters (unlike the two expansions). So you can delay Haven's Fall until you have no other choices. I haven't explicitly tried it, but I think you can do Haven's Fall any time before you start the Final missions (Gates of Hell, etc.).
What you are probably seeing is that you chose that path earlier in the game. So you don't have all the possible tech upgrades. Note that you can reach Haven's Fall on the eighth mission. Or wait until the twenty-third mission. Obviously the longer you wait the more tech you have.
In the two expansions, they changed things so that you don't need to worry about mission order. They always allow you the maximum possible advancement. Wings of Liberty still works the original way though.
The easiest way to do this is to play through a campaign on Casual difficulty, maximizing your tech advances. Then switch to Hard for Haven's Fall when you run out of other missions. That maximizes your options in-game for tech advances, etc.