There are certainly differing levels of sub-contractor relationships.
Sending some random out on a job that you picked up that day is one end of the spectrum as is requiring all insurances, reporting, guidelines, material selections, and best practices the other end.
States being up in arms about not collecting taxes, there is your most poignant motivator. I agree to the extent that sub-contractors should being paying taxes. To require companies to hire people as employees to resolve that issue is overkill in my opinion.
The organized subs in this market are incorporated and as squared away as most large companies. The reason people like that model is because they ultimately make more money.
Keep taking more money away from the people working for it, give it to the gov't to spend. I know I like that.