It's the statists final fall-back. That, and general welfare.
The founding fathers warned us about this.
/johnny
You're an aviation buff, right? Think about the quality of metals used in aircraft engines. That's not by mistake. The FAA inspects these parts to ensure that the metal is the standard of metal that is mandated by either statute or administrative rule.
What gives the FedGov the power to issue such regulations? The Commerce Clause? Why? Because these parts are bought and sold across state lines, and they're installed in aircraft that fly quite intranationally.
The same principle applies here. People selling certain grades of titanium are meeting standards that are established by the FedGov, just like people selling "extra virgin" olive oil will need to meet certain standards, or they can't call it "extra virgin".