Yeah, it's different because the money found on the guy is clearly evidence. In drug cases the authorities go far beyond seizing evidence. A better example would be if the DA seized the thief's bank account, if he had one, or perhaps some of his furniture.
However, I think we are getting away from the basic issue, which, to me, is state power over the citizenry.
I don't disagree with you on the need to lock up drug dealers. I am not in favor of giving the feds such an awesome tool as asset forfeiture, though.
For example, you'd have to be charged with possessing/distributing/manufacturing a minimum of say, $10,000 worth of drugs before asset forfeiture kicks in.