IMO, a beater isn't a bike that is ill maintained or abused, it's simply a bike that's scratched up, has lower-end components on it, and is a bike that you don't feel bad about taking out in the weather. That said, I guess that most of my bikes could be considered beaters (due to age and paint quality); however, the vast majority of them have mid to high end components...just components that are 15-20 years old! lol

As for a commuter, I go between three bikes (although here, it's 2) - a Phillips 3 speed, a Univega Activa with drops and 38c tires, and now, a '90 Fuji Palisade. They're all good, solid, very well maintained bikes, but they're older and, given my dirt road commute, rather dusty, even though they all get a wipe down once a week.

And yes, road salt is the devil. I can ride one of my derailer bikes (probably the 'Vega) 7 miles to work through snow and slush, let it sit in front of my desk, and by the time I go home (7-9 hours), I have to re-oil the chain because it is so squeaky from being eaten by salt. Every year I need to replace the chain on that bike after the snow stops. The Phillips fairs a bit better, but being that it has steel rims, you do have to watch for rust appearing on the wheels. This is with my once a week chain oiling regimen.