Creatives 'not too bright', claims client

I just received an email from a fellow creative. Said creative had been given a written brief, which still bore a list of hints at the top for whoever was writing it. One of these read as follows:

Brevity. Creative people are not too bright. [So] don't tell them what they already know and spare them what they don't really need to know.

This seems an extraordinary attitude, and made me wonder how widely it was shared. There have certainly been times when I've discovered that there was more information to be had than what I'd been given, but it never crossed my mind that the client might have considered me too thick to handle it.

What do you think? Is this a common belief, or just a rather hilarious aberration? Do tell in the comments (anonymously if you prefer).