Why not? Steve Jobs had a Mac Pro, why shouldn't Tim use a iMac, or high end Mac Pro? I'm sure for a portable device he may use the rMB but he could also use the rMBP as well.For whatever, reason, I'd guess that Tim Cook, as CEO would not really need a very powerful Mac, and so would deliberately choose to bee seen with the base model MacBook. After all, if you see him at an airport with one, wouldn't you think "If it's good enough for Tim Cook, it's good enough for me"?