Surprising Bogosity from PearsonHigherEd.com

Pearson usually supplies instructor supplements to texts in Zip archives. Fine. But the PowerPoint slides for Sebesta's Programming the Web 5th ed are in an archive with an extension .sitx. A little searching says this is a StuffIt archive, a proprietary format. Why? Are they going out of their way to make sure some of their customers can't access the materials? StuffIt's free unroller isn't even available in a Linux version, making the 10MB archive useless wasted space on my hard drive.