He's either really slow, or really smart. You generally don't see average kids pausing in their speech too much. It could also be a style of talking from some cartoon shows, I know they have a similar speech pattern. Could be many things, but to assume it's nothing seems a little foolish. But eh, your kid. Your problem.
He doesn't do it all the time. I think it's the style now. Its not a mental thing. I just think he gets excited over stuff. And why is it that everything turns into a "problem" when kids do things? I swear, I'll never understand it. Like when my daughter was born she was tiny, she's two and still kind of tiny. So, every time we'd take her to the doctor and he'd measure her and say, "Hrmm...well she's not anywhere on the chart." and I'd sit there and argue with him that what does his chart show? What is my daughter being compared to? And he'd say, "Oh, its this chart that has "averages" of children her age and she falls below some of the things on the chart." it'd freak my wife out and she'd start crying. One time he mentioned the chart to my wife and she got really upset and I looked at him and said, "The next time you whip that chart out I'm gonna shove it up your ass." Since then, he hasn't used the chart. My daughter is very healthy, talks up a storm, runs around, climbs all over stuff. So, his chart is crap.
My son is not [censored]. He just for whatever reason when he is trying to sound "cool" while telling a story he throws a lot of pauses in and it's really annoying. Normally, he doesn't do that, just when he is trying to tell stories. Geez.