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Still, domains with rewritten urls do seem to get deeper and more frequent spidering. I've seen this many times on various domains I've worked with. My guess is that obviously dynamic urls require extra spidering code to keep the bot from getting trapped. That in turn places an extra limit on the amount of attention and resources a site can get from googlebot.
I've seen google spider as many as 5 variables on our site. But it appears 3 is the limit for us currently.