Asmodeus is worshipped because he emphasizes stratification, discrimination, order and a shred of honor.
Stratification means there's clearly me, us, and them. There's people higher then you, and lower then you. Asmodeus clearly appeals to those people higher on the scale, who can then enforce their wills on those lower on the scale by Holy Writ, which means the 10% are entitled with all the power, and its completely justified. Why would they give that up? Asmodeus is a god of pure elitism, racism, sexism.
Those who don't have power don't even have the RIGHT to complain about it. Those not a part of the system are to be considered as little more then animals, do what you like to them.
Order means this is the way it is, if you don't like it, tough crap. Which is wonderful if you do like the way it is, with you on top.
He caters to the smart and the subtle instead of the strong. Laws, contracts, the ability to manipulate others...not just bash them over the head and take what you want. VERY appealing to the powerful and wealthy. If you aren't smart enough to stop me, it's your own fault, right? I'm just smarter then you are.
And of course, wrapping this all up in shreds of honor...you DO obey the law, you WILL keep your word, and you simply don't just kill and take...how savage! How ignorant! No, no, we will do this LEGALLY...
Like Fry said in Futurama, "I hope to be rich some day so I can abuse the poor smucks I used to be" or something like that. Someone at the bottom could learn to be an assassin, and start to kill their way to the top. Anyone too stupid to hire them and have them kill the obstacles to their success, is too stupid to live.