Steve,
The "use two key" version may also be a result of strict cryptographic
requirement. The services-that-be may well end up only allowing us to use
relatively short RSA keys for session-key encryption purposes. E.g. if I want
to send an encrypted message in France to you, I should pick one of your keys
wich is short enough (say, 256 bits) and use that to pass the session key. I
can still sign with my 1024 bits RSA key -- signature is not a problem. Our
local variation of key escrow, I suppose...
Christian Huitema