Since Dreamhost has a history of crazy sales/promos, I'd guess that it's just a temporary level-off period before the next trick.
Could be wrong... but I have a hard time believing they won't get an urge to burst towards the 1,000,000 domain mark.
No doubt that for now, it would seem geared towards slowing down new sign-ups and there are plenty of $22 customers they'd probably be better off without.
But at the same time, it does also lose good customers, since everyone likes money. If $97 promo codes were around when I signed up, I certainly would have used one... and I'd still be here several years later either way.
I'd be curious about any data they have on how many cheap sign-ups turn out to be good, renewing customers vs. the number that either a) leave after one year, or b) get booted before 1 year is up.
Maximum savings promo code: MaxSavingsAtDH