Just because you can't see the argument for a single bag doesn't mean that there isn't one. For example, when I recently traveled to Peru, I rarely let my backpack out of sight—I didn't random hostels enough to leave thousands of dollars of equipment there, nor did I have a vehicle. That said, I did very well with a single piece of luggage, the Calumet BP1500 Large Backpack. It fit my 13" Macbook Air (with plenty of room for a larger laptop), my DSLR with a couple lenses and requisite accessories, in addition to clothes and whatever else I needed to survive for 10 days. All with enough space to bring back souvenirs.
The simplicity of a single bag was a boon when cramming myself into a taxi colectivo for 2 hours with a dozen strangers. Honestly, I'm not sure there would have been room for extra luggage.
As for the author's request, most details can be found on the product page, but in my opinion, the best part of that bag was having a hip belt to take the admittedly heavy load off my shoulders while hiking.