Well, I have never come across a cellist breathing while playing the instrument. . .
You know they're breathing while they play, right? Otherwise, they'd be dead. That's a tongue in cheek response as I'm sure that's not what you meant.
A cello is a string instrument, not a wind instrument. Compared to other types, playing most of the string instruments is more similar to aerobic exercise. It requires quite a bit of stamina to move the bow like that and some of these instruments aren't easy to hold. Playing a musical instrument is also a form of communication so it makes sense that a cellist's breathing might be more noticeable during the most passionate parts. I agree though that sometimes it seems overdone and it can be distracting. Wind instruments require different breathing techniques for the most part.