I'm anti-noncompete too, but my comment wasn't normative, concerned with "pro" and "anti", "should" and "shouldn't"; it was just an attempt to describe the world. (Although my perception might be skewed by my own preferences, hopefully that hasn't made my description inaccurate.)
Anyway, from that perspective, what Paul Graham does or doesn't want me to do isn't relevant. I doubt he really wants me to do anything other than make insightful comments, since I'm not working with him.
What I'm saying is that the QA guy has more bargaining power if he can go work for your nearest competitor, and perhaps still more bargaining power if there is also no trade-secret law prohibiting him from taking that other information to the competitor, not just himself. (He can't do that legally in California.) So, all else being equal, he's more likely to move from Massachusetts to California than vice versa, especially if he's a really good QA guy who can get a job even when there's a lot of competition.
It might be the case that having access to really good QA guys are more important to your business being successful than being able to keep your QA guy from defecting. For example, maybe you're a good guy to work with, so the defecting isn't really a problem, and the difference between okay QA and really good QA is huge. In that case, you'd be better off doing business in California instead of Massachusetts, if that were the only difference between the two places.
On the other hand, if the thing that would make or break your business is being able to raise $500 million to build a semiconductor fabrication plant, you might find yourself siting it in Massachusetts (or Oregon, say) instead of California, in order to reassure your investors that they're getting the best possible deal from your employees.
So banning non-competes will attract certain businesses: the ones that are good to work for and in which employee skills are much more important for the company profits than, say, employee retention, secrecy, or capital equipment investment.
So I think it is especially knowledge and sales businesses that will tend to seek out areas with strong non-compete prohibitions --- not on purpose, but just because that's where the superstar scientists and salespeople are.