When people think back, they blur factors (like you are blurring adwords with googles initial success). I was there when Google took over, and it WAS as simple as I said.
They first had a popular search engine, and they built a good business on top of that. The business building part was complex, probably, but getting the search engine to be popular was just a front-end thing.
Googles speed was not relevant, Altavista and many other search engines prominently displayed how fast they were. There was a sort of speed competition at the time, so Google was not significantly faster than the others. Those other engines (like altavista) did not even have websites with lots of images or so, so it loaded just as fast as google.
Picking the right user-interface has been the reason for success for many companies. People will come and overcomplicate it later, but in the end, it was just the user-interface that made them win.