There are plenty of good reasons (from a corporate perspective) to have online authentication; all sales are tracked, all customers and their activities are tracked, they can practically guarantee first-hand sales and returns for DLC or additional content.
Then again, this sort of behaviour can alienated the consumer base. One ideal example is the Sony PSP vs the Nintendo DS; the DS sold a heck of a lot more units despite it's pricetag and technical inferiority (excepting the touchscreen). Its library of games was larger and it wasn't locked like the PSP. Even after the PSP was jailbroken, Sony's futile efforts of releasing and forcing firmware updates on the customers was a deterrent.
Instead of focusing on really moving units, Sony seem to always be preoccupied with locking down the hardware and software. I don't see any PC manufactures cracking down on what you can do with the hardware you buy.