Well, it was a little complicated what happened. Salvatore got screwed by the 4e time jump of 100 to 150 years, which meant that most of his cast of characters (Cattie-Brie, Regis, Wulfgar) were going to be dead. So he wrote a trilogy and at least one short story to deal with that. Cattie-Brie got hit by the falling Weave, which spellscarred her and left her in a coma. Regis got poisoned. Mielliki came personally to collect them. Wulfgar returned to his tribe, became chief, and lived a long and fulfilling life, spawning a large family. He went out as an old man barbarian should, fighting a remorhaz or some other monster, I believe. Cadderly Bonaduce took down a dragon previous villian that was merged with an illithid and resurrected as a ghost, but to do so he had to become a ghost himself to trap it. Captain Duedermont tried to reform Luskan and paid with his life. Only Drizzt and Bruenor survived, and Salvatore's first 4e novel Gauntlegrim dealt with the death of Bruenor and Thibbledorf Pwent, leaving Drizzt all alone.
None of this was what Salvatore wanted. In fact, it's pretty well known that he and Ed Greenwood, after hearing about 4e, immediately started plotting how to "fix" it all. So bringing them back just sort of lets him continue on with the plans he had, including Cattie-Brie's transition from a fighter/archer, which she was physically incapable of anymore because of a permanent leg injury, into a spellcaster, which she started learning from Aluriel of Silverymoon. It fixes the magic hole in the party, and I also like Regis now being an actual (and effective) rogue, instead of just some commoner schmuck who gets lucky sometimes to be able to hit some distracted thug over the back of the head with a mace.
And I will ALWAYS give mad respect to the death of Bruenor. That is how a dwarf should go out!
RAS always goes with whatever the edition change entails regardless if he likes it or not.
Let's face it it's not as if he has much else to fall back on.