You're the one attributing PF's success to sparing of sacred cows. The burden of proof is on you. I'm not saying that it isn't a reason for success; just that you haven't done much to prove it. You've stated an opinion and are now charging me with proving it wrong.
I think that keeping the cows is certainly part of the reason PF thrives - because those cows snare the grognards who don't want melee to have nice things, think that ToB is unrealistic and overpowered, claim that 4e killed roleplaying, and love Vancian casting, who make up a large part of its fanbase. Pathfinder does thrive on them, at least in part... because they're part of its marketing strategy, not because they make for a good game.
There are, however, plenty of successful RPGs out there that do away with the sacred cows. For a quick and dirty look, let's check out the examples Robby listed:
What sacred cows are there?
A short list:
- Alignment (mentioned a few times already)
- Plus items
- Six ability scores ranged 3-18.
- Hit Points
- Armor Class
- Vancian Casting
Nearly all of these are specific to D&D and games based on it or its OGL content, so you only need to look at games that aren't D&D to find games that ignore most or all of them.
For a few examples, Green Ronin's Mutants & Masterminds does away with Alignment (doesn't exist), Plus Items (everything comes from the same pool of points, no matter the shape it takes), Hit points (uses Toughness checks instead), and Vancian casting (it can be modeled, but powersets are inherently dynamic and at-will unless you make them otherwise) in its second edition. How close it sticks to the six ability scores is arguable, since those are mostly aesthetic in 2e with the exception of Str and Con. Its third edition moves farther away from the six ability scores, ranking them directly by their modifier and introducing two additional ones for a total of eight, but is still obviously based on them (including in its range of ranks, which starts at -5 and lists 0 as average). Last I checked, M&M was very much popular and thriving, with a fair-sized and dedicated community.
The various Storyteller game lines published by White Wolf do away with Alignment (WoD and its subgames use a scale of morality which, while retarded in its own right, doesn't have anything to do with D&D's nine alignments; doesn't exist in Scion and Exalted), six ability scores (Uses nine attributes ranked 1 to 5; the specifics vary between WoD and Scion/Exalted), and Vancian casting ("magic" abilities are generally based on a pool of points like spell points or power points and are otherwise usable at will if you can spare the points). Hit Points and Armor Class are sort of kept in spirit, if altered with health levels and Defense/Armor (WoD) and Defense Values (Scion/Exalted). The degree of deviation is similar to that of M&M 3e's abilities to the six ability scores, I guess. Plus Items exist in the form of equipment bonuses or artifacts. WW games certainly are popular and possess a huge fanbase, as much as it boggles the mind.
FATE-based games do away with Alignment (doesn't exist), six ability scores (skills only, ranked on a theoretically open-ended ladder), hit points (stress and consequences, which represent wounds as a narrativistic abstraction, are used instead), Armor Class (opposed rolls are generally used), and Vancian casting (varies between games). Plus Items are debatable, in that they theoretically are defined in the rules, but I haven't seen them used in practice beyond weapons and armor (which don't work as a straight bonus to X roll). Though I can't say I'm certain as to individual games' popularity, DFRPG has a decently-sized following, and the FATE system as a whole strikes me as something of a comer.
