They generally don't add DLC for BTA games later on since it would be useless for anyone who DIDN'T beat the average.
Humble THQ bundle gave DLC to Red Faction Armageddon.
Red Faction wasn't a BTA game in it though, so anyone who got it before the DLC was added but didn't BTA already had the base game. Adding Sims 3 DLC on the otherhand would be useless for anyone who already got the bundle but did not BTA. Totally different situation.