I recently applied to become an affiliate for a physical product. I was not declined out of hand, but was required to sign a document stating that the only promotion I would do would be to place banners on my existing website. They specifically prohibited me, as a NY affiliate, from promoting them actively in editorial content on the site, or in email messages, and no PPC either.
It seemed to me that their lawyers decided that if the company reduced the affiliate's role to nothing but a media placement paid on a CPA basis, then they avoided the state's claim that they had a business nexus in NY, and therefore avoided having to collect tax from NY buyers.
If I wasn't going to actively promote them, it didn't make sense to even bother. Based on their payout, and typical banner clickthrough rates, I'd likely make less that AdSense was paying.
I don't know how common this is among programs. But it definately sucks. And of course, some other companies refuse to allow NY state affiliates, which sucks only slightly more.