It is a form of protection of the IP, in this case, the magazine contents. It is normal for most paid for downloads of this type (e-books and even other magazines that offer a download version will block you from printing a copy of it).
Well said, Triverse. This is done to 1.) prevent piracy / file sharing, and 2.) the digital version is far cheaper than the print version. Imagine how people who pre-ordered the print version would feel if someone downloading the PDF version at $1.95 could print their own copies; it wouldn't be right. Plus, this would also create another problem; the potential of unauthorized copies of the magazine circulating without publisher approval would be immense.
That all makes sense. I am just disappointed that i wasn't able to buy the printed version.
I hope in the future the printed version is available to purchase for longer