Nobody seems to like posts that say "the Terrans are too good," so don't worry. I don't think the Terrans are too good, I just think the Orbital Command is too good.

It is the obvious choice for upgrading a Command Center. When you reach the point in your game that you want to upgrade your CC, your choices are OC or PF. What kind of choice is that? The OC is so good that there are hardly any games in which a Terran player doesn't upgrade as soon as he has a mere 150m of discretionary income. A single MULE more than pays for that, and MULEs alone would make OCs worth the effort. Add to that a scan that very well might save your ass if you absolutely need detection or some instant recon. Not that it even remotely needed it, but you can get extra supplies anywhere, too.

But we all know how great MULEs are.

Planetary Fortresses are used for cheesy rushes or, sometimes, for defending remote outposts. If you're relying on a PF to save an expo, though, that expo is probably already lost. But, to be certain, a PF is definitely useful if you're trying to hold off some hellions or roaches. But shouldn't PFs be good for more than defending some expos some of the time against small numbers of ground units? It is more likely, even on those remote expos, to see no upgrade at all on a CC, or even a second or third OC, than it is a PF.

Maybe if it didn't mean giving up on the Orbital Command, an upgrade costing 150m instead of 150m/150g and containing some of the Terrans' most powerful mechanics, we would see players choosing the Planetary Fortress. As it is, there isn't a choice at all, because no one can afford not to make an Orbital Command. And RTS is about making choices.