This is quite a silly statement. You can still screw up a test with expensive equipment. You can still NOT do a test that you should have though of. That said, this whole thing is no big deal. I'm surprised so many Apple fans have such a problem with it this criticism though. They doth protest too much.
One of the things you learn in customer support is that for every person who complains, 10 more stay silent. I’d take a 0.5% call rate for dropped calls as meaning 5% actually have the problem.
And note that Apple was careful to mention calls to “AppleCare”, NOT to AT&T. Most people who have dropped calls tend to call the carrier, not the hardware manufacturer (when your call drops, do you immediately think of your carrier or the phone maker?).
If Apple’s getting 0.5% of all iPhone 4 owners calling THEM over dropped calls, that’s a pretty significant rate overall. How many called AT&T about the issue?
A more telling metric than what Jobs reported would be the total number of iPhone 4 users who reported a dropped call - not just to AppleCare, not just to AT&T, but worldwide (since the sales are reported worldwide). THAT would be a relevant statistic; calls to AppleCare is interesting, but I don’t think too relevant.