I actually disagree with most of your post. Full disclosure: I’m in the social sciences/health sciences, but still a field where postdocs, research faculty, research scientists, etc., are very common.
In my field, a research scientist is quite different from a postdoctoral fellow, as are the attendant salaries. Research scientists are either 1) people hired on grant funding to do a specific set of tasks in support of that grant, usually under the supervision of a PI (who is generally tenured faculty at the institution), and thus the job is often term-limited unless the scientist and the PI write a new grant together, or 2) 100% soft money jobs at centers or institutes in which the scientist writes their own grants to keep themselves funded. Postdoctoral positions are traineeships; postdocs often have tasks that look like research scientists’ tasks, but they are considered in training and under the supervision of a mentor. Postdoc salaries range from $40-50K whereas research scientists/associates salaries are usually like $60-80K. (New tenure-track faculty in my field generally start at about $80-95K at R1 institutions.)
Research scientists are actually more equivalent by level tenure-track assistant professors in my field; they are independent, they usually have at least a modicum of control over the direction of research (and full control if they are one of those 100% soft money positions), and they usually aren’t using the job as a stepping-stone to a tenure-track faculty position. Postdoctoral jobs are understood to be temporary steps on the way to a faculty position, which is why the pay is so low. Current NIH levels for first-year postdocs are like $39K.
And research faculty/fellows are something else altogether. Research faculty are exactly that - faculty who don’t have to teach; they only do research. At most universities they are non-TT but it is possible to be a TT research faculty member. And a research fellow can mean anything. There are some very senior, distinguished people who take Research Fellow positions for a year or so while they’re on sabbatical from their main job.
I’m…not really sure what your vested interest is in trying to prove that PhD Comics is outdated/outmoded. I just graduated from graduate school in August 2014, and I find the depiction to be a somewhat accurate portrayal of graduate school - although of course exaggerated for humor, just as Sheldon, Leonard, and Raj are exaggerated for humor in The Big Bang Theory. (Although, let’s be fair - we don’t know what their titles were before Sheldon got promoted to assistant professor. (Sheldon also has two doctoral degrees and finished college and his first PhD in the 5 years between age 11 and age 16, so BBT isn’t exactly a bastion of real-world accuracy.) It does sound like Sheldon, Leonard and Raj are research scientists, but then again Sheldon got his PhD at 16 and was a visiting professor in Germany before he turned 20…so I think it’s safe to say that his career might have taken a different turn than the typical real-world scientist. Even in the real world, exceptionally well-prepared superstar graduate students can go straight into faculty jobs. (Also, it’s pretty clear that Sheldon was supposed to be an extremely absurd depiction of a quirky super-genius scientist.)
I also had the same observation as @cosmicfish. I mean, Sheldon and Leonard share an apartment, and none of the characters appears especially wealthy or even upper-middle-class (other than Raj, who comes from a wealthy family).
I don’t know what field Mike Slackernerny (the grad student/postdoc with red hair in the comics) is supposed to be in, but it’s not unrealistic that a graduate student make nearly ten times what he made in grad school depending on the field. One of my former students just started a sociology PhD program in which the stipend is $18,000 a year; if he got a job at a management consulting firm in 6 years, he could very well make nearly $180K a year. Again, it’s exaggeration, but a top grad student making $35K at MIT or Caltech or something could very well go to Google or Apple and make many times that, and probably more than he could expect to make as an assistant professor.
The tl;dr point of all this is that the graduate school - postdoc - assistant professor model does actually still exist and is flourishing in many fields, and salaries for postdocs are still actually pretty low.