"It's strange. Some coder working for free can come up with better stuff than a multi-million (billion?) dollar company [can]."

It's not strange at all. Blizzard's developers have to answer to half a dozen different departments, each of whom has a separate idea about what the functionality should be ("Bob, I like your idea for the floating combat text, but some of our users are color-blind, and they won't appreciate the multi-colored text blending into the background; reduce it to primary colors, mmkay?"); they have a user base that's simultaneously much, much broader and much, much less responsive; and the responses they do get tend to be along the lines of "X feature sucks, it should be like Y addon" (or "X feature sucks because Blizz stole Y addon") instead of actual constructive criticism. Addon developers, by contrast, have the luxury of a user base that's specifically interested in what they're working on, and they don't have to report to anybody except the users, and that only if they happen to feel like it.

That, and players tend to ignore the mods they don't like in favor of the mods they do like; whereas it's hard, if not impossible, to ignore features of the default UI (without using mods to cover them up!).

So, no, it's not strange at all that a coder working for free can produce features that you like, whereas Blizzard is going to be hit or miss as far as you're concerned.