The Rental Argument is bogus and here's why:

Since the Computer Software Rental Amendments Act of 1990, it is illegal to rent computer software, unless you get strict permission from the publisher. Now because of this, it can safely be assumed that the consumer, when they go to a store to purchase said software, they are indeed purchasing it, because the availability to "rent" that software is extreamly rare.

Therefore, while they may own the code and the right to use such code, claiming that "software is only rented and that they control and license every allowable use," is at best distorting the rights granted upon purchase of software. If that was the case, couldn't they prevent users from uninstalling said software, claiming it is not within the user's rights to do that?

I suspect the court will side against Blizzard on this, if only that otherwise it could very well upset the basic meaning of copyright, and fair use in the software industry.