As pointed out before, Happy Days went another six seasons after the shark jumping. Liking the whole run of Happy Days does not make you a bad person. Nonetheless, it would be difficult to deny that something changed in tone along the way.
I think WotC jumped the shark with D&D with Races of the Dragon. There were so many things wrong with that product. First, it took what started as a bit of lore in 3e ("kobolds believe they are the chosen followers of dragons, isn't that cute har har") which evolved into canon in 3.5, and in Races of the Dragon, come full to fore, with dragon-winged, definitely spawn of dragons, kobolds. Kobolds??? Seriously??? Then you have the Spellscales, which is arguably one of the least cool-looking DDM figures I can think of... and the Dragonborn. Whereas before draconic beings were typically monsters, Dragonborn were a PC-race. In addition to shifting the D&D milieu somewhat by making them a racial choice, they also emphasized a relationship with Bahamut (a platinum dragon) rather than "normal" dragons, and they were a transformed race rather than a natural one. Yet these characteristics proved to be quite superficial, as 4e proved with its monotreme dragonborn with oddly non-monotreme-mammal breasts. The book itself was created from the premise that books with "Dragon" in the title sold well, racial books sold well, and if D&D needed anything, it was more dragon. As such, the book was decidedly un-artistic. Races of the Wild may have been mediocre, but at least it was something. Races of the Dragon was little more than an attempt by the writers to redeem a cash-driven concept.
Despite the changes in specifics, Races of the Dragon began to develop some of the tropes that would come into full bloom with 4e: draconic kobolds, exotic (even transformed) races, dragons all over the place, and a hard shift away from class genre fantasy as well as baroque fantasy, and straight toward the gonzo fantasy that grew out of video games, endless FR novels, blockbuster cinema, and cross-polination with works such as Exalted and Earthdawn. Note that this transformation has little to do with what I imagine to be the financial rationale for Races of the Dragon. Rather, it has to do with the writers, unfettered from what has come before, deciding to make D&D its own thing... and its own thing, as they saw it, involved a lot of tropes I would identify as being foreign to the core of the original game.
So, to summarize... the financial pressure to produce something with mass market appeal, combined with a gradual but noticeable shift toward a new style of fantasy, contributed ultimately to 4e and thence to the development of the line since.