Sal Glesser's comments regarding the popularity of serrations on Spyerco knives are interesting. Why do you suppose serrations are so popular? I've given some thought to the matter, and here are some observations.
There are some cutting tasks where a serrated knife works better than a plain-edged knive. Cutting stiff plastics, for instance. There are also a number of tasks where serrations don't make much difference one way or the other, such as cutting tape. And of course, there are tasks that are virtually impossible to perform with a serrated edge, such as cutting a wide sheet of paper off of a roll, or scraping things, or chiseling thin materials against a hard surface.
If I am to carry only one knife, it will always be plain edged. If I'm to carry two knives, the second one might be fully serrated. But I hate combo-edges. I have only owned one combo-edged knife (a Benchmade Mini-AFCK), and it made me so mad I gave it away. In my opinion, a combo-edge is definitely NOT the best of both worlds, as more often than not the serrations actually get in the way.
So, why are serrations so popular? I think it's because the average plain edge, as owned and used by the average person, is pretty dull. So maybe the average serrated edge really IS more effective in the majority of instances. Perhaps this explains the relative popularity of serrations on Spyderco's cheaper knives: the more expensive knives are bought by people who know how to maintain them to the point where serrations cease to be a significant advantage.
Here is something else to consider: It often happens that people don't have the immediate option of buying the plain-edged version of a given model. Many times I have shopped for knives and found that the local dealer only has it in combo-edge or fully serrated. The explanation is that "combo-edges are far more popular". If people who don't care one way or the other see only serrated knives on display, and are told that "it's what most people buy these days", then they too will end up buying it, and the cycle perpetuates itself.
Now, there are some knowledgeable knife users on this forum who have tried all kinds and still prefer serrated or combo-edges over plain-edged knives. Be that as it may, I'll bet most serrated or partially serrated knives are bought by people who: (a) can't or won't sharpen a plain-edged knife to give it a fair chance; or (b) don't see a plain-edged version of the knife they are interested in.
Now I'll end this diatribe with an aphorism: People like combo-edges for the same reasons they like McDonald's "special sauce": somebody told them it's special, and it's the only way they can get a Big Mac.
David Rock