Affiliate programs are just another form of advertising, often referred to as performance marketing / performance advertising.
Merchants surely look at their affiliate expenses as advertising related expenses. They know their ad costs, profit margins, cost per visitor, value per visitor, conversion rates, etc. They know everything they need to know in order to switch to another form of advertising.
The only thing these bogus "affiliate nexus" laws will do is cause companies to shift their budgets back to non-affiliate type advertising. And I call them bogus because an affiliate is in no way a part of the company.
On the other hand, I don't see how Amazon gets away with not paying sales taxes in States where they do have a real physical business presence established.