It does seem rather bad business for them.
I mean if their users drop their address numbers down to below 2000 just in order to suspend their account they likely won't re-add those addresses later when they need to renew since the whole thing is a massive hassle.
Plus a $9 cancellation fee is going to leave a bad taste in most people's mouths which they'll remember when it comes time to send e-mails again, I know it would me.
And all this for what in return? To make $9 once? Lose potential repeat custom for $9? Meh.
It is their business so their choice. I'm sure they have run the numbers on this to see if it makes the most money, but I try to avoid companies that operate like that (both in my professional and personal life).
Just for one example, a DVD rental company (similar to Netflix) make it SO difficult to cancel their service when I wanted to rent DVDs again I decided to take my business elsewhere, since the competitor let me start and stop it online as I wanted...
So it might discourage some from cancelling their subscription but once people do successfully cancel they will never return, because you never forget how big the hassle was to cancel it.
It is just classic MBA short term profiteering where they pretend metrics like reputation and long term growth don't exist. Just as long as THIS year looks grand.