Businesses now have to compete with open source or decentralized services that cut them out. When money enters the equation, people immediately start shopping, they start asking "Is this an expense that is necessary?"
That plus the amount of uncertainty john q public has on transmitting money online (a reticence I share to be honest), makes paying small fees a large barrier to entry.
Besides, if I've learned anything, I've learned that just because you paid a company money, doesn't mean they won't turn around and sell you up the river. The barriers of trust for a service that's free and non-free are exactly the same.
Google and Facebook are not in the document copying business. They index, curate, store and generally make information easy to access. That's a real service which costs real money to offer, and is not going to be just spontaneously overtaken by some FOSS equivalent (whatever that even means). And they could charge real money for it, if they wanted. Personally I would welcome that opportunity if it meant they would treat me more like a customer and less like an ad demographic.
Barriers to entry for these tools are: the technical expertise to setup and run the programs (which is low low low, but still enough), and the obvious lack of users to give the system meaning.
You can get around bandwidth bills through distribution. open source is very good at that.
Was? It still is. The number of companies that rely solely or primarily on advertising to generate revenue is pretty small compared to those that charge their customers.
I suspect you're almost surely right when it comes to the number of companies, but I'd be far more interested in seeing analysis on this broken down by volume of dollars / revenue.
For instance, most (all?) professional and even college sports, TV shows, numerous web companies, etc. -- tons of ad revenue, though perhaps relatively small number of companies, but is why I'd be curious to see data on this if you know of any?
We don't really need to filter companies that are solely or primarily dependent on advertising. We can compare the entire amount of money spent on advertising (which is a superset of what we're really looking for) versus everybody else (which is just total revenue minus advertising revenue) to see it's not even close.
One source[1] for global ad spending puts it at $467 billion (for 2010), I couldn't find more recent hard data but another[2] estimates it at $581 billion for this year. Let's assume the estimate was right and round up to $600 billion.
WalMart had revenue of $476.3 billion last year[3]. You can combine WalMart and any other company in the top 10 of Fortune's Global 500 and their combined revenue would exceed total advertising revenue[4]. The combined revenue of all 500 is $31.1 trillion[5], even if that included every penny of ad revenue it would still be a ratio of 50:1
[1] http://www.wpp.com/wpp/press/2011/dec/05/groupm-forecasts-gl...
[2] http://www.statista.com/statistics/237797/total-global-adver...
[3] https://en.wikipedia.org/wiki/Walmart
Maybe I'm misunderstanding...perhaps you were referring only to businesses selling access to a web service?