Facebook's success certainly cannot be attributed to their "idea": the online community thing had been done thousands of times before. Just never executed well enough.
Google's success cannot be attributed to their idea, as there were numerous search engines before them. Execution is what propelled them to the forefront. Their search engine actually showed good results.
Amazon. They sell books. Not the most novel idea out there. They just did it better than anyone else. Zappos. They sell shoes.
For all the time people spend comparing their startups to the biggest players, it's quite odd that so few realize that it's not about the idea. It's about the execution.