Well, that's not entirely the case. Certainly if you're talking about the highest levels of editing, on feature films, national TV, commercials, etc. you're pretty much looking at Avid, with Final Cut Pro making small but significant gains every year.
So why Avid, and not anyone else? Well they were pretty much the first out of the gate with useable non-linear editing. The hardware and software costs were at the time so expensive that only production companies and rental houses could afford them. So Avid was entrenched at the high end, with various workflows, and data formats grew up to surround these machines that are still in place.
For example, on the last feature I worked on, the video that was telecined from the 35mm print came with the telecine information in the standard .ALE format (which stands for avid log exchange). I'm sure that you could get that info translated into another file format, but you can get .ALE's right out of the machine, so why bother?
If you do aspire to work at the high end, learning Avid is pretty much a necessity. It can be intimidating and counter-intuitive for someone used to another package, but once you have the program down, it's extremely fast to edit with.
Besides at the end of the day they're not paying for an Avid Operator. They're paying for an editor. Which buttons to push should always be secondary to your skills. And you should strive to keep current with any new technology that helps you use those skills. Which is why so many Avid editors are learning Final Cut Pro at the moment (and also complaining loudly about it). :)
John Burkhart
Editor-in-Chief
Videomaker