FWIW informit.com has the same model. We have regular holiday sales, update our eBooks, and offer the different DRM-Free formats including PDFs.

Informit.com is a Pearson owned site and sells the following tech imprints: Addison-Wesley, Prentice Hall, Sams, Microsoft Press, Cisco Press, Pearston IT Certification, Big Nerd Ranch, Peachpit, Adobe Press, and New Riders.