Actually if you do double blind tests you will find that Bing and Google are indistinguishable. We did this at Blekko earlier with our "3 card monte" gambit where you did a query, got back blekko, bing and google results, and got to pick the one with the "best" results for your query. Blekko usually won if it was query we had a slashtag for or if it was a "highly contested" query (lots of ad spend like "no fee credit card" or "cheapest insurance") In the former case our curation meant that more results were appropriate, and in the latter case our spam filtration left us with better results. If it was a general query for which we didn't have a category for, and it wasn't highly contested, google and bing split the results, often 40/40/20 sometimes as low as 35/35/30. And if it was a long tail query like "turnip growing in south philidelphia" or something very specific with few sites associtated with it, and we didn't have it in a slashtag, Google would "win" those. Microsoft borrowed our idea and did their whole "bing and decide" campaign.

Many people realize that if you put Google ads on Bing's results and Bing's ads on Google results the profitability would switch (not that I am entirely sure what that says other than having a credible search engine and top end Ad inventory is required to make excess money in search)

It will be interesting to see if Marissa gets back into the game with Yahoo when their agreement to use Bing results for Yahoo searches expires.

The interesting linkage is that you can't sell search advertising unless people send the search request to you, and if you're not the most common place that people search, you're unlikely to get first shot at advertising. You can "buy" traffic (that is called Paid Distribution) by putting your search box on people's web site, or causing someone's browser to send you search queries first, or paying a phone maker to send you all their search queries, but you have to make enough money from the ads to offset what you pay. And as I mentioned over the last 8 years Google has been paying more and more for their traffic (up to $968M last quarter) and very few entrants into the business are going to compete with that. If you already have a platform (like Mozilla has Firefox, Apple has the iPhone, Facebook has pretty much everyone's Facebook page) so you "own" the ingress point, you can leverage that with a good search engine to make a lot of revenue. But if you need to pay for access to the ingress point, and pay a big chunk to the ad provider, it is really hard to support a lot of infrastructure (which is proportionally expensive to index size). That is the constraint box of search today.

The interesting thing for me is that every quarter, of the last 16, Bing has been making more money per click and Google less, that cost equation is balancing out. That is going to put a lot of pressure on the non-core parts of Google.

To answer your question, Google succeeded well when capturing the value of linkage data to extract page relevance (the original Page Rank patent), they created an advertising incentive which made their algorithm break (you want a billion in-links to your page, no problem! say the black hat SEO folks). Google is still making tons of money on search but you can look at their performance over the last 4 years to see the air is coming out of the balloon. What comes next is still an open question.