I think johngenx was replying on of the comments on the article, not the article itself. Sometimes people depend on apps (like google maps) that use cellular data to display the map instead of storing the map data on the cellphone itself. I have a feeling that this is what has led to people getting the impression that they have to be within cell range.
My biggest issue with cellphones is operating them in a storm. While a good case can make the device fairly water resistant, cellphone touch screens generally stop operating once they get too wet. This is not a critical issue, and I have used mine in storms before; it's just a bit of a hassle.
google maps can be pre-cached to operate out of mobile data range, but there are many better apps, as we all know. one of the best in my view is Alpinequest or Everytrailpro. Alpinequest has a good open source world wide map in the app and you can easily pre-cache many other maps for your selected area, before you head out. You can even pre-cache microsoft Bing maps satellite imagery.
Spot on about bad weather and smartphones. not a good mix. also, battery life of good GPS units tends to be a lot better than a smartphone