Several people on sci.crypt have pointed to the following paragraph in Matt Blaze's report of the NSA briefing on Clipper, posted here and in the newsgroups:
Clipper chips should be available (to product vendors) in June. You can't just buy loose chips - they have to be installed in approved products. Your application interface has to be approved by NIST for you to get your hands on the chips.
This could explain a lot. In particular, if they can enforce this, it could put an end to the dreams of multiple encryption. For months people have been saying, "Clipper? No problem. I'll just encrypt with PGP then pass it through Clipper and the Feds won't ever guess! Ha, ha, ha!" Maybe this won't be so easy. From Blaze's description it sounds like such devices wouldn't be approved. It could be the only Clipper phones will be ones that don't do anything to keep the Feds from picking up the conversation. People could still build non-Clipper encrypting phones (assuming that the constant rumors of threatening midnight visits from NSA agents are false), but the users of those phones could no longer blend in with the Clipper traffic. Hal