As a webmaster it is easy to get caught up in what you know from your experiences, however your average Joe does not possess these sam qualities.
Your average internet user/surfer doesn't know why or how sites are indexed and listed on search engines.
Yahoo gets more traffic than any other search engine company, more traffic than MSN, and Google.
--However--
Yahoo is used for more than just searching the internet, there are many things you can do when you get to the Yahoo home page, from chat to shopping, to paying your bills online, email, and so much more.
(same for MSN)
Google--- Has only one thing in mind when you get to the Google home page, and that is for you to do a search for whatever it is you are looking for.
Because google is used primarily for searching it has become the Search Engine for your average joe.
All the search engines have their flaws, they grew really fast, in a short amount of time without much research to go off of, considering Search Engines were not really even know untill the 1990's.
In 1992 there were only about 20,000 websites on the internet, it wasn't untill the dot com boom in 1996 that brought the internet to life.
Now all the search engine companies are taking all the information they have gathered from there 10-15 years of being online, and learning how to improve the way we use the internet.