I know this is an "after the fact" kind of thing, but that's the idea of Comprehensive coverage. What that does is your insurance company pays the bill THEN they fight the other company for the percentages and such. I've been in a situation almost exactly like that; my insurance paid the full bill and then duked it out with the other driver's company.
I might be sticking my neck out but I work for an insurance company (on the computer side) and may have some insight. (Ducks and covers as things come flying at me...
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Having said that, it's not necessarily that the insurance company is the problem but how they compensate their claims adjusters. Claims adjusters generally are compensated for keeping their claim amounts as low as possible. (Hey, I need a bigger check this month so let's see who I can stiff - it DOES happen folks.) And insurance is one of the most regulated industries in the country so just about everything they do is wrapped up in legal "red tape". Write to your political representatives and tell them you wish that claim compensation stuff would be stopped to prevent this kind of crap. See, I'm convinced that if the claims adjusters were just paid a straight salary, it would reduce most of this "your fault, his fault" stuff anyways.
As a side note, where I live in Maine, a parked vehicle is NEVER at fault; the moving vehicle ALWAYS is. Some of that stuff might be the legal system and not the insurance company. Either way AT, I feel for you. Dealing with those issues always sucks and you NEVER get compensated for any of the crap you have to put up with - even if they pay all the bills.