"There are certainly valid business reasons for Apple to offer the service for free" 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.
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.