1 : Black can deviate once white played h3, he can choose Na6 first for example then e5. Na6 being the main variation in h3 systems.
2 : anyway, does h3 really helps white in exchange variation?
For instance, in this game :
This is the model game given by J.Gallagher in his Starting out KID. White can improve in this game (15.Nc4 was a mistake, 0-0-0 was better and led to slightly better endgame for black). Gallagher tells that h3 wouldnt really improve white's position and indeed, black didnt use g4 square.
And as u pointed out, possible that black can try to use a variation where there is not Bc4 move, so Na6 makes the job here (again, but i like this move very much in KID).
2 examples (playing in blitz but who black's play seems easy) :
c6 is also a possibility, but it can transpose into Na6 anyway, another example :
I think KID players are usually happy to see exchange variation. It is really more easy to handle than big lines!
Moreover, those playing it are usually players refusing the fight, they play passive and i am not sure it is a good idea against black's set up which after all, has a better pawn structure...
I have a general question about the exchange KID. I think the opening is relatively promising for people who enjoy playing endgames and trying to grind out slightly better positions. Why do most people who play the KID exchange play 6. Be2 instead of 6. h3? In the mainline it just looks like white gets the extra move h3, which can't be bad for white.