On some level, I think Howard resents Jackie's talent. And Jackie would stand up to Howard from time to time while Artie is more of a pushover.
I remember just before Stern went to Sirius, they had this couple's contest on the show. Artie and his girlfriend won. Howard was such a baby because he felt that his girl was "close enough" on the question of preferred salad dressing that he ended up making a big stink. It was one of the most pathetic and petty things that I've ever witnessed. Artie just caved.

Personally, I lost interest in Stern once he separated from his wife. He turned out to be a total phony and complete hypocrite.

He used to rail against Hollywood. He'd make fun of celebs all the time. But the truth is that he just really wanted to be a part of that world and was pissed that he wasn't included.
Then I'd hear stories that he was partying with celebs in Malibu, going to fancy parties in the Hamptons, etc.
He used to rip on John and Gary for going to baseball, football and basketball games. Then he starts showing up once a week at MSG to see the Knicks. I remember once he was sitting next to Paris Hilton.

That's when I knew it was over.
He'd yap about how great his wife was. The movie was basically an ass kiss to her. Then he cheats on her with a girl from SCORES (he denies this) and boom, the marriage is over. Then he gets this new bimbo who wouldn't be anywhere near that warlock if he were Howard Stern, accountant.
He claims he'll never marry again and then what does he do? Barbara Walters at the wedding? Trump? I had to finally face it: Stern sold out. So I am glad this satellite radio experiment has been an utter disaster. He's nothing now.
Having got that off my chest, I must say that have no ill will towards Artie. But the dude is seriously self-destructive. He clearly hates himself and he really needs some help.