Why do you need proof? Tell your "web guy" to do it or he's fired.
Geeze!
http://www.google.com/webmasters/guidelines.html
Quote:
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Allow search bots to crawl your sites without session ID's or arguments that track their path through the site. These techniques are useful for tracking individual user behavior, but the access pattern of bots is entirely different. Using these techniques may result in incomplete indexing of your site, as bots may not be able to eliminate URLs that look different but actually point to the same page.
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