Yeah, I think you're absolutely right. Insurance really drives this, too: HMOs, especially, are constantly pushing for GPs to receive less and less for a given procedure. Combined with the role insurance companies play in (effectively) deciding what a patient does or doesn't "need,* insurance post-1990 has been trying very hard to convince doctors to do a
worse job.
My father, for example, had a practice for over 20 years in a small, working and lower-middle class town. He was notorious for taking patients in late and for long waiting times. And everyone wanted to see him. He was also notorious, as it were, for consistently finding and correctly diagnosing issues that other doctors failed to find. He talked to patients about the health in detail, with physicals often taking an hour or more. He would "forget" to charge folks who he knew were struggling to make ends meet.
For over ten years, this worked fine. My family was, frankly, rich, with yearly salary approaching $200,000 dollars at times. Starting in the 1990s, my father ran into HMOs, head-on, if you will. Over the next ten years, his monthly salary consistently decreases until his overhead exceeded his revenue, and was forced out of private practice.
Now, my Dad might not have been the model of an efficient capitalist, but he was a damn fine doctor. I, at least, think it's a damn shame that we live in a world where that kind of care is systematically eradicated.
So, yes, I think it is that GPs deal with "less expensive" issues, but that's also because they deal with every issue. The goal of a medical system should be to avoid entirely expensive issues. The fact that specialists are employed frequently enough (i.e., demand is high enough) that their labor is worth so much is a systematic failing of the medical system.