Powell and Donovan fill the same position in these robot stories as Bert and Ernie do in Sesame Street: they teach us things, but they're also meant to make us laugh. And Powell and Donovan are also expert robot technicians, just like Bert and Ernie.
In fact, Powell and Donovan have a classic comedy set-up, just like Bert and Ernie (and Abbott and Costello and every other comedy duo): Powell is calm and does things according to the rules (Runaround.1); Donovan is fiery and lets himself get carried away (Runaround.1). You can also tell them apart physically: Donovan has the classic sign of a fiery temper—red hair; and Powell has a mustache. (As usual, the calm person is often driven crazy by the emotional person and by robot problems, so Powell spends a lot of time pulling at his mustache.)
This difference in character leads them to approach their job differently, which is really on display in "Reason": Powell argues with Cutie about reason and evidence, whereas Donovan threatens to hit Cutie (34) and later spits on Cutie's God (95). And yet they always get the job done, all while joking about how they hate the job. (Check the banter between them when they look over the ship in "Escape!" for an example of that (87-121).)
That's at least one thing to consider: Powell and Donovan aren't as good as Calvin (probably), but even though they're very different than her (they are silly while she is serious), they get the job done. They are, as Lanning notes, the "top field men" that US Robots has (Escape.68). So maybe, when we read Powell and Donovan, we're reminded that you can do your job and be a little humorous at the same time. You don't have to be a robot when dealing with robots.