"If the national Main Street Fairness Act passes it would impose a national tax standard but allow states abiding by the Streamlined Sales and Use Tax Agreement to force Internet sellers to collect tax."
[ETA: The author may have meant the Marketplace Fairness Act, which does have an alternative in place for states not participating in the project. There are two bills in each house, so it is confusing.]
_What_ national tax standard? This sentence should have said, "If the national Main Street Fairness Act passes it would authorize states abiding by the Streamlined Sales and Use Tax Agreement to require Internet sellers above a size set by the Governing Board to collect sales and use taxes."
_That_ would have accurately (altho inevitably incompletely) described the act. Also, Amazon, Home Depot and Wal-Mart is not an odd alliance. It is an extremely sensible alliance, all of whom stand to benefit from this arrangement, because it would drastically reduce (over the long haul) their tax compliance liabilities, in part through the project's amnesty provisions and in part through the indemnification provided by relying upon state supplied information and/or CSPs.