piatkow - 1:30 pm on May 24, 2010 (gmt 0)
Different registrars may have different rules. What TLD (.com? .uk? .de? etc) and what country are you buying in?
Paying EUR for a .com or USD for a .uk may catch you out with exchange rates.
Another alternative is that you had a cheap deal when buying other services which is no longer offered.
I am assuming of course that you aren't confusing the domain and the hosting charges.