You counting ONLY endgame raid content and counting number of bosses, not the level of difficulty and amount of time it take it to loot it's corpse.
You don't matter, that 15 bosses of Naxxramas at the beginning of Wrath was so much faceroll, that it could be cleared in the first two weeks of playing lvl 80 even for a noob.
And you don't care, that 4 bosses from VoA are even more faceroll than Naxx was. And for you, ToC, as a 5 man raid, was equal to BwD, or even more, because Nefarian was also boss in Vanilla. You don't care, that these was two extremely different battles?
WotLK provided us, like, 4 oneboss raids (if we count VoA - after presenting another giant there, nobody care about previous one), which were as easy to down, as possible.
That's about raid content, which is in my opinion - better in Cataclysm.
But we forgot about another part of Cataclysm content - leveling in Azeroth! If we try to count leveling areas in wotlk, we will have one modified part of existing area (Eastern Plaguelands), and 8 and half (crystalsong forest) areas in Northrend. Oh, I forgot - and one battle zone, Wintergrasp.
Cataclysm completely rehashed (with changing of geography, quest chains, npc's, flight paths, lore, and sometimes - contested zones changed into horde or alliance) content of almost ALL (Almost - except TBC starting zones and Sillithus) Azeroth zones, added starting zones for new races, and 5 high level zones (one of them is like subcontinent, Vashjir split into 3 parts). It is 20 Kalimdor zones, 24 Eastern Kingdom Zones, Vashjir, Kezan and Lost Isles. And Tol Barad.
48 new zones with quest chains vs 8 and half? Damn, Wotlk was small!