I don't understand why a chess based scoring system would ever be used for pool.

Andy,
The chess scoring system was chosen, I am guessing, because it works. It is simple to understand, simple to administer. Could you imagine all of us drunk pool players trying to keep track of innings, safety shots, 8-ball scratches, 8-ball pocketed in the wrong pocket, etc...? How many times have you heard someone say "Was that a run? I don't know. How many times did he shoot? No, I think the other guy pocketed a stripe on the break." or something to that effect. We simply don't have the manpower, will, or dedication to adopt a pool-specific ratings system.
Also remember that the ratings were introduced to the league simply as a novelty, a fun little perk to playing in a bar league on Wednesdays. They were not initially intended to become the focal point that they seem to have become. So, adopting a chess scoring system seems pretty resourceful.
I personally don't give a fiddler's fart if extra points are awarded for runs, since I rarely get a run. In fact, I get somewhat giddy if I have a 5-ball run. As far as not losing points if I am the victim of a break and run, it doesn't really matter to me either, because it has not happened to me all that often. If you consider how many games you 'should have won' but didn't due to an some unlucky occurrence, and how many games you won, even though you had every right to lose it, those points all seem to come out in the wash anyway.
I guess my point is this: the ratings work fine for what they are intended - to provide us with some fun way to measure how we are doing in the league and perhaps motivate us toward self-improvement. They are not used to handicap matches, and they don't win or lose us money. They are simply a fun reference. Modifying the system is no problem, if that's what the majority would like, but I can't agree that the rating system was a bad choice because it was designed for chess.
And next time, Arno, don't scratch on the 8.

Lenny Erickson

The rating system works great as is. Keep it simple loss or win. Just like at night at the bar. If you win or lose the next player on the list plays. Extra points to be rewarded for 8 ball runs would only give certain players inflated scores and no loss of points to 8 ball losers would be less interesting. How else are the good guys going to care when they lose or how else are they every going to lose points. Just like at the bar you are off the table with a loss by 8 ball run and the loss of points is equal to your time loss on the table. It's a gamble and fun.