Naaa... all hosts oversell--and DH can actually back up what they offer.
The ones that do the most crying about how evil overselling is are people that can't compete on that level.
If you were to monitor a hosting site like webhostingtalk.com, you'd see the most people seem to define overselling as, "anyone that offers more than I do for the same price or less."
I think it's just another funny, yet effective, marketing gimmick. It's not like it drops enough to matter. They can sit there and keep lowering stuff, while still offering more than the competition. Plus, like already said, it doesn't even affect you when you use a promo code... and it continues to grow back as soon as you sign up anyway.
Save up to $96 at Dreamhost with ALMOST97 promo code (I get $1).
Or save $97 with THEFULL97.