That was the question I considered while listening to HubSpot's Brian Halligan discuss the Round D funding the company had just received from Sequoia Partners, Google Ventures, and Salesforce.com, among others.

Of course, the question didn't pop into my head out of the blue. It was sparked by a comment Brian made regarding the Web. Specifically, he said that Internet-based businesses needed to "go big or go home" because the Internet is starting to look like a "winner take all" marketplace.

Conveniently, he could point to his new investors as two examples that proved his thesis: Salesforce dominates the CRM space, and Google is, well, Google. HubSpot would like to follow in their footsteps and become, as co-founder Darmesh Shah put it, "the single emergent platform provider" in the marketing automation space. When you are THE platform for a specific kind of service, essentially, you've won.

While understanding the ambition and appreciating its audacity, and even seeing how it might unfold in the case of HubSpot, I keep asking myself if the statement is really true that the Web, or at least the world of Software-as-a-Service, is really "winner take all."

At first glance, I would say this is more or less true. Granted, the Web is a big place, and taking it "all" is a practical impossibility. However, within certain limits the Web definitely looks very "winner take most." Are there other search engines? Yes. Do people use them? Yes, millions do. Are they Google? No.

The fact of the matter is that when you become the dominant service provider online (THe place for search, THE place for auctions, THE place for community, etc.), you will tend to stay dominant and even grow inexorably through sheer force of inertia. The more people use your service, the more valuable it becomes; the more valuable it becomes, the more people are attracted to it. It's a virtuous circle.

But is such growth and dominance perpetual? We have in our memory once dominant (or, at least, very big) players who have shrunk or vanished. Netscape. AOL. MySpace. What is to prevent Facebook or Google from suffering their same fate?

A couple things, actually. On the one hand, Facebook, Google, eBay, LinkedIn, YouTube, Amazon, and Twitter have enjoyed a very different kind of success than that of those they vanquished. In other words, their fates have already diverged. On the other hand—or really the same hand—their sheer size and reach make it, with each passing day, more difficult for upstarts to dislodge them.

Still, Web consumption habits do change and fragment. Remember, the Web itself is continually growing as more nations and communities come online. Thus, even the success of the companies named above has to be relativized. Facebook may have 500 million active users (depending on how you define "active"), but with close to 2 billion people on the Web, that's still leaves 75% of users off Facebook. To think about what that means consider this: There could be a "Facebook" out there with 1 billion users that you've never heard of. Seriously.

But here's where I think Halligan has a point. Think back to the way Microsoft Office became the dominant "productivity" suite. It all started with the ubiquity of devices (PCs) running a certain operating system (Windows). Since "everyone" had these devices, everyone had Office. And if you wanted to work with or even communicate with a business, you had to have Office too, even if you were running Macs. The size of the user community drove more and more people  to join the community out of necessity. Even now, with numerous word-processing alternatives out there, the docs that people share with me are Word docs.

The Web is the new "ubiquitous device" and just like people only needed one word-processing program and one spreadsheet program, they only need one search engine, one social network, and one micro-blogging platform and, perhaps, one marketing automation suite. And the more people flock to one particular solution, the more that solution becomes the ONLY solution.

So, you can see the power and the allure of creating a platform, rather than a mere application. Indeed, it's the same logic that drives Amazon, Apple, and others: Why be a shop when you can be the marketplace? Why limit yourself to making money off transactions that you alone conduct when you could get a cut from every transaction?

Yet, at the same time, the fact that others choose to build for your platform or sell via your marketplace points to the most significant way that the Web is not, after all, "winner take all." Why not? Because every platform creates a new "all" with new opportunities for building apps, communities, ecosystems and even, if the word makes sense, "meta-platforms." (Facebook, as a kind of alternative Web sitting on top of the traditional Web, is a perfect example of the latter.)

In other words, the Web may look like a zero-sum game from moment to moment—and there are undeniably winners and losers—but the Web's very openness, and specifically the openness created by emergent platforms, means that the sum is perpetually growing and there is always more "all."

What do you think?