Isn't a joke "alive" until the explanation? So those that 'got' the joke would've enjoyed the joke, before moving onto read the next line. So reading the explanation of the joke wouldn't interfere with their enjoyment of the joke since they already enjoyed it prior to reading the explanation.
If you're telling a joke, you don't want emotional context switching. A quick explanation, laughter might be preserved (so the above pun may or may not inhibit the execution of the original joke).
But every joke has an emotional gravity and the longer you compliment it with other emotions (e.g. intellectual explanations), eventually escape velocity is reached and you're in an entirely different emotional state.
For those who do not get the reference, Alan Kay is the inventor of SmallTalk: http://worrydream.com/EarlyHistoryOfSmalltalk/