I posted the question because I trip across some variation of this quote all the time (most recently Jimi naming Garcia and Jimi naming Irish guitarist Rory Gallagher) and I've often wondered whether it was true or merely apocryphal. I recently ran into a guy who lives in (nearby) Pasadena, Ca. at a local guitar shop. We were talking and he had an interesting variation on the story, insisting that the quote is attributable to Clapton. He provided 2 interesting details.
First, that David Letterman asked the question on his tv show.
Second, this fellow claimed that he had personally spoken with the guitarist cited by Clapton - who, after some prodding from a third party to their conversation - reluctantly admitted that the story was true. The guitarist in question had joined the ministry and was serving as the pastor at his local church! His name is Caleb Quaye and he was formerly guitarist with Elton John and later, Hall and Oates.
Can't be 100% sure it's true, but the guy who provided me with this account seemed pretty convincing.
BTW, other answers may be true, as well. I'm sure both EC and Jimi were asked the question more than once and variations of this may have been the preferred response of either or both.