"So... to answer your question. There is unlikely to be substantial difference between the contracts that you sign at various companies in the US working as a programmer or in the law that applies."
Joel's main point is that, even with CA's labor code, it can still come down to a gray area around what a company's "business" is.
What I think the OP is pointing out is that in NY a company is able to set up a more restrictive contract than a company. At the very least (and from personal experience), companies in NY can introduce more gray areas in the contract (making it more difficult for entrepreneurs to feel safe in working on weekend projects) while still making it seem as if they follow the spirit of the CA labor code.
http://answers.onstartups.com/questions/19422/if-im-working-...
tl;dr from the post:
"So... to answer your question. There is unlikely to be substantial difference between the contracts that you sign at various companies in the US working as a programmer or in the law that applies."