sporky_rat is correct! We originally planned to only sell seed accounts once (at launch) and then never again; we had to hold another sale last year after being unable to accept payments for 3 months (so 2010 had 12 months of expenses but only 9 months of income), but that was an unexpected thing and it took us a lot of handwringing before we decided to do even that. (You can read some of our thoughts on the matter in the old pre-launch business FAQs -- the short version is, it's actually really bad for us to be selling seed accounts, because even though it means a short-term cash infusion, it also means that there'll be long-term support costs and no guarantee of ever receiving another payment from that account.)

Because we knew we weren't going to put them on sale regularly, though, we were careful to design the account levels so that a seed account and a premium paid account are functionally identical, in terms of what features they get. There's nothing you can only get if you have a seed account (except of course not having to pay again).