Yeah, the first half of the year is rather lackluster while the second half is pretty heavy hitting with the start of the summer sale, then we have the halloween sale (which while isn't too big still is usually ok as the weeks just tend to be a week long), then we have the black friday/thanksgiving sale, and finally the holiday sale which happens to last about a week or so into the new year.
I guess it is hard to throw a sale in the first half when there really isn't any types of events to throw it around. So they fill in the voids some with little indie weeks or publisher week/ends.