It also bears mentioning that ZKC (and the original run of Hayate) aired Sunday mornings, IE a very very very VERY desirable timeslot. Just about everything that airs then tends to be very well produced since that's the time to seize children by the throat and sell toys . In comparison, most other anime airs some time after midnight, will have horrible ratings, and be expected to make up the money on DVD sales.
If you need an object lesson, Kekkaishi's a great one. Went from excellent production when it was stuffed behind Detective Conan in primetime, to abysmal when it was moved to late night.
And pfft. Fanservice. What did you expect given the OVA's title?
And more caps if you're impatient.