No, it's not. When you zoom, your field of view gets smaller, and when you walk, it doesn't. Moving closer just makes your subject closer and therefor larger. If you find an angle you like but you can't zoom in enough to get the shot, say, standing on the knuckle of a jump, you're fucked. If you walk in, you lose your angle, and don't have the same shot. There's nothing wrong with primes, I love them, but you need a lot more lenses to cover the same focal lengths as one zoom. To illustrate my point:
1. Put zoom lens on camera
2. Look at a subject and zoom in
3. Then, walk towards the subject while zooming out so it remains the same size in the frame
You'll see that the perspective changes. Sometimes, its ok, but other times it ruins a shot. I know some filmers use the walking in while zooming out technique to get a certain effect on the perspective while still maintaining the same subject presence in the shot.
