The move is not surprising. There has been a general move away from printed books and magazines already. This includes a migration of advertisers hence a thinner Electronic Design magazine than in the past.
Unfortunately the move to the web has not always been an improvement. Part of the problem was the lower resolution and smaller screen sizes. This has been changing but the HTML delivery mechanism has not improved substantially from a presentation perspective. The big problem is that the content is no longer the delivery mechanism.
True, scaling, panning and all sorts of options abound but this is mostly to address inadequacies of the presentation as well as the poor content creation mechanisms. The other issue these days for magazines, and readers, is the ubiquitous advertising and sensory overload a content management system (CMS) presents. Menus, multiple columns and even animations are all over the place adding to confusion and distraction.
On the other hand, Digi-Key, like most vendors with an online presence have sophisticated websites. They often have extensive search mechanisms and the ability to compare items. It is not always easy to get these things to work but they would obviously be unattainable if they were in print.
In a sense, the disappearance the printed catalog coincides with the rise of the tablet. PCs and laptops grew the Internet but they are cumbersome to move around. Yes, laptops and netbooks are portable but they pale in comparison to tablets for portability and general viewing.
The big challenge and question in the future will be whether any of the benefits of an in hand, printed item will be brought into the tablet age. It was an easy task to tear out an article or a page from a catalog when you wanted to save something. That is significantly harder with an online system. Likewise, you can carry a printed item anywhere. An online interface needs at least a WiFi connection.
There are other things I'll miss from the printed catalog that I don't get, although it is possible to replicate, with the online version. For example, flipping through a catalog just to see what might crop up is not something that is easily done online. Likewise, bookmarking can be a pain in the neck. Yes, there are browser tools for this but just try to mark the middle of a video or a Flash-based page. I often need to hit the Print Screen key just to save something.
In the long run it will save Digi-Key money and save a lot of trees. They used recycled paper already but they also have lots of customers. Still, it is sad to see things like this disappear into the ether.