A lot of companies have business models different from our expectations.
Some big examples are Gillete, in the business of selling razor blades; HP, in the business of selling ink and toner cartridges; Or even McDonalds, which lives of the rents it collects from his tenants, the restaurant franchisors.
I'm a very happy user of the Dropbox service, but I don't get their business model.
Their core technology is the sync engine, the best I ever used, not because of its speed, but because of the transparency and simplicity of the entire process: you drop your files in that folder, and all your devices will get it.
But all their marketing for both free and payed accounts is based on storage space, a commodity.
I pay for a lot of online services. Some, like Github and Flickr, I don't even needed to do so, because their free versions would be enough for my usage. But I keep paying because I want those companies that are providing me with a valued service to prosper and succeed.
I cannot do the same with Dropbox, although I probably use them more than any other service. Their focus on pricing their solution on something that is a commodity, and not their core technology, devalues my opinion on them, and prevent me from giving them my money.
I would gladly pay them for the sync service itself, without any server-side storage, because thats the part that nobody else was able to provide to me yet, in the same simple and efficient way.
But I can't: for some reason, they sell you storage, and you get this sync service for free. The only thing I can do is to use their votebox and hope to see a plan focus on sync, not storage space.
I really don't get their business model...