My fanboy explanation of why Kirk beams down on most landing parties is because thats his style. He likes to get the lay of the land. He's more like Captain Cook than a modern Navy Commander. And unlike say Picard he's young enough and fit enough to do it.
Let me just step in here and point out that Picard was probably more fit in his Golden Years than Kirk ever was in his prime! Stewart's certainly more fit than Shatner, even in these days. But he had to be, did he not? To secure a Pretty Young Gold Digger, a Sugar Daddy must be fit in body ... and bank account. Stewart is also a superior actor than the Shat, in every way. For example, Picard's kicked ass on many a planet ... and found love with many a young woman in a tight, short skant - all whilst quoting Shakespeare in an authentic British accent.