I think a really thorough discussion of Internet sales taxes nearly violates forum rules because some of the really "newsworthy' stuff relates to proposed legislation. Thus, it's a little tricky to talk about this stuff. That said, and honoring forum policy, let me say that under current law generally if a business has enough of a connection to a state, the business needs to pay income taxes to the state. Further, the business needs to comply with other state tax laws such as those relating to excise and franchise taxes. (Sales taxes are excise taxes.)
Things that create nexus, currently, include having property in a state, employing people or contractors in a state or doing stuff like providing services in a state. And what's going on here in terms of public policy is that the federal laws protect businesses from taxes and as importantly the tax accounting costs of state tax laws as a way spur and support interstate commerce.
One relevant issue here and something missed by people who don't have to do the tax returns is the tax accounting or compliance cost. E.g., people can say stuff like, "Well, don't be a crybaby about the tax accounting... computers and software make this work easy."
But imagine if you did not one state income tax return... but, say, forty state income taxes returns. And then to make the comparison really fair, imagine not doing this once a year, but imagine doing it every month which is often required by excise tax rules. I.e., a business if not careful about nexus maybe would need to do 40 excise tax returns a month. The business's customers may pay the sales taxes but who will pay the accountants?
To circle back to the original poster's question, one can understand why the business feel they need to avoid nexus by doing things like severing arrangements like the one described.
P.S. Actually because the page provides some of the primary source authorities for the current tax laws that control how Internet sales tax works, I'm going to post a link to a page that describes the current situation and, gulp, some proposed stuff that would not be appropriate to talk about here. Moderators? please forgive me if this indirectness also violates forum policy and of course edit or have me edit the post. Here's link: http://www.stephenlnelson.com/remotesalesalestax.htm