For me, saying that TWF needs the -2 is like saying you need to take a -2 on using an exotic weapon to balance it with martial weapons.
Even if TWF is better, you still have to take a feat to make it effective, and in this case you need 2. It SHOULD be better....but realistically even with no penalties to hit its still not always the optimum choice:
1) You still only get half your strength bonus to damage on the off-hand.
2) Its only useful on full round attacks.
3) You don't get the benefits of power attack (and DR cleaving) as you do with THF...and you don't get the AC of sword/board.
Even if TWF is better, you still have to take a feat to make it effective, and in this case you need 2. It SHOULD be better....but realistically even with no penalties to hit its still not always the optimum choice:
1) You still only get half your strength bonus to damage on the off-hand.
2) Its only useful on full round attacks.
3) You don't get the benefits of power attack (and DR cleaving) as you do with THF...and you don't get the AC of sword/board.