Locking folders have been around for a very long time.
The Spanish Navaja dates back into the early 1600s.
http://en.wikipedia.org/wiki/Navaja
Tough as heck folders with blades in the 3" to 4" range have been the choice of working people in Europe for centuries. Consider the German "sodbusters" and the French Opinel to name just a few.
Big "folding hunter" designs have been in the state for a very, very long time as was the large Barlow. And of course, the Buck 110 was, for many years, the top choice among working men, soldiers and sailors and biker gangs.
All of this to say, there have been different approaches to the problem for a very long time.
As much as I'm fascinated by the beauty of normal sized slip joints, my big XL hands and my near daily use of the knife for food prep and wood working make the Opinel #9 my preferred EDC carry (combined with a Leatherman Micra).
EDC Pair by
Pinnah, on Flickr
I do more than an average amount of backpacking trips and ski touring trips and to be honest, an Opinel covers 99.9% of my backcountry knife needs.
Just watched a nice video by AverageIowaGuy on YouTube last night on expedition knives and he compares the various knives he used and saw used on 2 of his Amazon treks and concluded a locking folder with a blade between 3" and 4" was all he needed (well, he also carried a parang). Conrad Anker who knows a few things about being outside carries a Bladeo, if I recall correctly.
I find slip joints too small and fixed blades too big and bulky and a locking folder to be just right.