Why Microsoft's Yahoo bid makes sense

(Fortune) -- With Google's stock already down considerably in recent weeks, the Web's next two most powerful players today struck a powerful blow for equality and influence in the increasingly-important Web ecosystem.

Microsoft controls a huge and multifaceted Web presence, and retains still-almost-unlimited financial resources. The combination of all that with Yahoo's superior Web brand and deeply entrenched position as a marketplace for display advertising and online media is probably the only one that can begin to match the Google machine.

Search remains the Web's best business. That's where the lion's share of ad dollars are spent, and Google controls more than 60% of it. Together, Microsoft and Yahoo will own almost 30%. If they can hold onto it that's enough to be a meaningful competitor. And since search is a game of scale, the two combining companies each acquire exponentially greater power than either could command on their own.

Like buyers and sellers of goods on eBay, both buyers and sellers of search ads want to do business where there is the largest number of counterparties. If there aren't a lot of sellers you don't want to buy ads from Microsoft, or anyone - except Google.

Both Microsoft and Yahoo have also been working to address this problem by acquiring impartial ad-marketplaces in the last year. Microsoft stunned the world by paying over $6 billion for aQuantive, signaling for the first time how serious it was not to be left behind by Google. Separately, Microsoft still exercises unparalleled influence on the devices that the people of the planet use to connect to the Web. Its monopoly on desktop software remains essentially unbroken despite inroads from Apple (AAPL, Fortune 500) and open source. And in the all-important area of mobile it has in the last year or so shown it finally is getting traction from handset makers worldwide, especially in the developing world and China.

As for Yahoo, it still hangs on to its bragging rights as the most-visited set of sites on the web, even though Google has been threatening in recent months to overtake it as its strength, particularly in developing markets, grows and grows. Finally, the financial resources of Microsoft could prove critical for keeping Yahoo's businesses viable in the face of the Google onslaught. Very few companies can afford the billions in investment - especially in data centers and infrastructure - that will be required going forward to compete globally in search, advertising placement, and mobile content delivery. Yahoo (YHOO, Fortune 500) alone simply didn't have the cash. Microsoft (MSFT, Fortune 500) does.

As Imran Khan, analyst at J.P. Morgan Securities wrote in his note on the deal this morning, "A combination of Yahoo's relationships and Microsoft's applications and devices could create a very well-positioned competitor" for Google.

All media is slowly moving towards the Web, along with advertising. The complexities of targetting, delivering, formatting, and promoting that content grow ever greater with the move toward mobility and as television too gets pulled towards the Web. In the all-digital world we are entering, the distinctions between on-Web and off will increasingly disappear. So to command the marketplaces and platforms for digital content is, for both tech and media companies, the most important mandate.

Wonderful as Google (GOOG, Fortune 500) is, the world and the entire Internet and media industry needs for its power to be countered and, if possible, matched. Without genuine competition everybody loses. That's what drives innovation. Even Google may benefit because if its share of search and online traffic grew much larger regulators would almost certainly begin to find ways of restraining it.

Today we've seen the beginnings of a bi-polar Internet, one that will influence and rearrange the competitive alliances and strategy of just about every company that aspires to a digital future.