"Magazines" are a specific form for delivering content that evolved out of the technological limitations of paper printing, the economics of delivery, and the whim of the market. Delivering them on floppy disks was tried, didn't work. Delivering them on CDs was tried, didn't work. These days, most magazines have web sites -- in some cases, the paper appendix has withered away, or is not as current as the online version. That's as it should be.
It's nice that they were experimenting with bundling their magazine up as an app, but unless they have a focus aligned with the delivery platform (i.e. MacUser being distributed through the Mac OS X store, iTunes Music Review via the obvious) there's no good reason to do it that way.
No, PDF is basically digital 'paper.' However, publisher-end tools and workflows can produce multiple PDFs from the same content for different form factors.
HTML5 and related technologies probably have the most promise in this sector though due to the large amount of cross-device styling and customization that can be done with CSS3 and JavaScript.
PDF's don't even work well on my Kindle, let alone my phone. Half of the PDF's I have for research are taller than my screen at a readable size, but inexplicably two-column. PDF is not the ultimate solution to portable documents.
>PDF's don't even work well on my Kindle, let alone my phone.
Then your Kindle is not a full featured reading device. The Kindle's opted to imitate a black and white textual book (the e-paper thing), when future ebooks can are will be much more than that.
