Difference between Zoom and non-Zoom lenses?

Nonetheless that's why they put a lens mount on there. It doesn't really take very long. I don't recall ever missing a shot during a lens change but I suppose it's possible depending on what kind of shooting you do. Of course, the same could happen while swapping a battery pack, which takes about as long.

I used to carry bodies with different films - but these days, I just dial a different speed on the same digital body. Changing film in mid-roll was possible but was pretty time-consuming and error-prone.

That hasn't been my experience. However it really depends on how picky you are. Many SLRs today are used as fancy snapshot cameras where it won't matter at all. That's something you need to decide for yourself.

From the reviews that I have read this is not the case. And having talked to photographers who have been taking pictures for many years the same thing is said.

You get sharper images on a prime lens. This in addition to the lighter, smaller advantage is what keeps them around. Why would you carry three or more prime lens if you could get the same shots with one zoom? You wouldn't. But when I look at the pros out there they have primes attached to their cameras.