Well, it depends on what cup, what coffee, and your body weight. If you're a skinny dude downing a venti from starbucks every morning, you're in a world of difference than if you brewed a lighter blend and drank from a small coffee cup.
I found myself quite addicted drinking a grande from starbucks every morning. Before that cup I was pretty much useless.
I just checked McGee's _On Food and Cooking_ (highly recommended, especially if you like Good Eats), and he's uncharacteristically vague about the effect lighter and darker roasts have on caffeine content. (The 2004 edition just mentions the weight loss during different roasts, pg. 443.)
I'm pretty sure you're right, though AB has been stubbornly wrong about enough things before that I prefer to fact-check him.
Also: If your love of kitchen science extends to mad science, you might also like _Wild Fermentation_ by Sandor Ellix Katz. Making sauerkraut, sourdough, mead, beer, tempeh, miso, etc. Best cookbook, ever!
It seems the difference is very small regardless of which one has more.
I'll have to check out both books. Good Eats has inspired me more than a few times to spend a Sat. afternoon attempting to recreate what I just watched ;) It would probably help to have something a little more concrete in front of me.
I found myself quite addicted drinking a grande from starbucks every morning. Before that cup I was pretty much useless.