To be honest, both the original WoW and TBC shipped with quite a lot of bugs. And some of them have still not been patched. It's still possible to fall through the world and there are still geometry bugs in battlegrounds (not to mention other zones).

Maybe we're just making the "legendary" polish a bit too legendary by not remembering how these releases went.

Sure, Blizzard releases great quality games - there's no question about it, but it's important to remember their releases haven't been trouble- or bugfree. I think it's mostl failures from other game companies that have made Blizzard look very good in comparison.