With Steve Martin, it's like you're a guest of a friend at a friend in the afterhours bar of an exclusive jazz club and just happen to be sitting next to Steve Martin; for most of the time, he's turned away, holding court, discussing art and music and LA, but every once in a while he turns to you and deadpans a funny line, which is by no means great in and of itself, but it's Steve Martin, you're next to him, you're a bit drunk, and you love him, so the joke makes you warm and happy. You know that if you repeat it the next day, you'll get a patient smile in response, but it doesn't matter.
Peter Serafinowicz, however, approaches you in the harsh glare of broad daylight in the middle of a crowded pavement, comes up to you - no, looms over you, and says with Pinterian menace in his brass baritone, "I'm going to make you laugh seven times today." And you think, "Well, a) that's impossible, and b) you've not exactly put me in the mood," and then he makes you laugh seven times, and, even better, after the first couple, you're completely on his side.
Is that how you see it?
UPDATE: Typo in title; sigh.