RE: Is cpim-srv document necessary at all? (Re: NAPTR and CPIM)

I don't really understand the rewriting of the IM URI. Why is it
necessary to turn im:[email protected] into anything else? Surely if I
do an SRV lookup and discover that, say, I should use SIMPLE then isn't
it obvious that when I send a message to im:[email protected] that it
is a sip: message, after all, I'm using SIMPLE? Where would the URI need
to appear? If it stays as im:[email protected] then doesn't Graham's
mapping issue disappear?

Adrian.