What I meant was that you can use normal one handed weapons with two hands to get the 1.5str bonus to damage. Like, I have a warhammer and a shield. If I drop the shield, I deal more damage with the warhammer per strike. So if you fight a foe with large DR, you can drop your shield and get some damage through.
I didn't mean the exotic becomes martial with 2h part that KOTC doesn't have, as you said.
The point was, that might as well use a feat to get Bastard Sword as a useable weapon, then depending on the situation, you can use it to mimic a greatsword(in that you use it with two hands, and the damage of a bastard sword, while lower than a greatsword, is higher than a longsword), or use it with one hand(or dualwield it with huge penalties). For one extra feat, you can get a weapon that can do many things. If you just used feats to make your greatsword using better, you could never use it with a shield as the game doesn't have Monkey Grip as a feat.
And I believe the ability to use weapon in several ways is valuable, especially if you're lacking in feats. Just use all your feats on Bastard Sword, and it can perform many functions. While lesser than a greatsword normally(as a 2h weapon), it is better if you have a weapon focus and spec and crit for it(than if you used greatsword without feats). Thus, you save the feats you'd otherwise have to use to get a two-handed weapon that performs well, if you also want to use a single weapon sometimes. Not to mention you don't need to waste gold and exp to forge different weapons, you can perform all functions with the same weapon.
Of course, if you'll never be using a shield anyway, then greatsword is the way to go.
Me, I like my versatility.