Yeah, Blizz learned something from paladins and forgot something from them while designing DKs. Both stem from the combat system they use (melee + spells).
First, scaling. Paladins spells scale by spellpower and they get a SP convertor in talents. DK abilities scale by AP since this convertor is built into the class itself.
Second, hit tables. Both classes have abilities that are treated as spells, but paladins don't get resists - because there's no holy resist (barring some odd "of holy resist" greens.. and I think they only appeared in Vanilla). DK abilites, however, can be spell missed, resisted and partially resisted. To top it off, the few abilities on the spell hit table are absolutely crucial in PVP combat, the DK interrupt and snare (the silence and grip are propably there as well).
While I'm still rambling on this subject, they should finish transforming thunderclap into a pure physical ability, now that it does physical (ranged hit table) damage it is a lot better, but you still can't use it while silenced.