In response to Dave Winer, yes, this is generally true. The longer coffee beans are roasted, the less caffeine they contain by volume, because the beans expand as they roast. Dark beans tend to contain less than lighter roasts. This also varies by bean variety; arabica beans have more caffeine than robusta beans, etc...

You can of course, make up for this in the brewing. Coffee made in a French press tends to have more caffeine than drip coffee.