Then it's a shame the article can't come up with any. The ones listed are either guesses ("might sell more devices") or counter to Apple's established, and highly lucrative, business model.
The fact's are.. They wont. Remember, it's the small additions to sales that make sales highly profitable and if they made it free, people would probably register for many accounts and use them to host warez. The .Mac servers are already slowly crawling along. By making it free, they would probably grind to a complete halt.
The author also fails to recognise that unlike Google, Apple's core profit model isn't advertising, instead, Apple actually does the opposite (wastes untold amounts on advertising). So Google profits heavily from their web apps, whereas web app's actually cut into Apple's profits.
Great in practice, but in reality, terrible idea. In fact, I'd be as bold as to say this article is as terrible as the idea..
Do people host warez on Dropbox accounts (in the Public folder)? Those are free and easily obtainable en-masse; you don't even have to keep the files on your own computer if you unlink the account after loading it.
1) A slight jab at Google. Right now I have my mac address book, iPhone, and Google address book all syncing OTA. It was a bit of a PITA to setup, but works now. If Apple offered the same service for free I would most likely switch.
2) Making the service free could add another selling point for macs, iPhones, and iPads. A "buy this item and you also get into another exclusive club" type of thing. The problem with this reason is that Apple doesn't seem to need to do this right now since demand already seems quite high at the moment.
My guess is that mobile me will not be free anytime soon unless Apple rolls out some new base technology that requires MM to function.