Citizens of Colorado are supposed to know and obey the law and apparently citizens of Washington state are expected to as well, if they are visiting. Why is it unrealistic to expect a Colorado police officer to know the law?
The theoretical answer to this is that citizens are expected to know all the major laws that govern everyday activity, and are then expected to educate themselves when they engage in a particular activity or line of business that a reasonable person would expect might be specially regulated about more obscure laws that might apply to that activity. Officers, on the other hand, have no way of knowing what sorts of violations they are about to encounter when they go out on patrol. I don't claim, though, that this is always true of fair in practice -- I'm just relaying the conventional reply.
And I think some perspective is in order: the officer's information was, at most, a few weeks out of date, and he did not attempt to actually enforce any Uber-related law. Also note what I pointed out in my edit: the new law includes regulatory restrictions that the driver may well have been violating.
That is actually a public interest issue. If an Uber driver hits you, and his personal car insurance doesn't cover it because it was commercial use, he can just declare bankruptcy and leave you stuck with the bill. This is why states require you to have insurance before driving.
Indeed, the irony of the article is that the police officer is the one who had the author's interest at heart. When a driver gets into an accident and a passenger is injured, the driver's insurance pays for the passengers's medical expenses. If the Uber driver's insurance denies the claim because he was engaged in commercial use (and probably lying about things like annual mileage and purpose of the vehicle), then the author is up shit creek.
And as you say, the officer probably found it odd that there was a passenger riding in the back of an apparently private vehicle.
I agree that this was a rather unfortunate and odd experience, but I don't see what the big deal is. The only thing that struck me as "really weird" about this is that the author called a Denver Post reporter to get live legal information while he was in the car, and that the author wrote this sentence: "Did I really want to take a ride from an individual who clearly lied to me, then was evasive when I asked one basic question?" (Did it ever occur to the author that the cop might just have been mistaken about Uber's legality? Did it occur to him the the officer was just trying to do him a favor?)
At the end of the day, we have a cop who pulled an Uber driver over for speeding and, though he mistakenly thought Uber was illegal, nonetheless only issued a speeding ticket and offered to drive the passenger to the airport. The author goes out of his way to pain the officer as behaving "really weirdly," and I suppose I don't see why the officer needed the passenger's ID (though I also would not be surprised to learn that it is totally normal for an officer to request a passenger's ID), but for the most part this seems like everyone did their jobs properly.
Of course, in a perfect world, an officer would know everything about Colorado law. But that is clearly unrealistic. So while yes, of course, it would be preferable for an officer to be properly informed about Uber's legality, I don't think we should be judging him too harshly for his mistake, especially when it sounds like Colorado has only recently legalized Uber, and the officer did not attempt to ticket or detain anyone for the purported violation.
Edit: By the way, the Colorado law imposes a number of requirements. Companies must obtain permits, drivers must display various notices and "[t]o obtain permits, the companies must have drivers pass criminal-background and driving-history checks. The drivers' cars must pass vehicle inspections, and be clearly marked as ['transportation network company'] cars. The drivers must also carry personal car insurance, in addition to the commercial insurance Uber and Lyft provide." http://gazette.com/uber-lyft-become-regulated-in-colorado/ar... Nothing in the article on whether Uber, or his Uber driver, has complied. The officer could well have been correct (though perhaps not for the reason he was thinking). Here's the bill itself: http://www.leg.state.co.us/clics/clics2014a/csl.nsf/fsbillco...
Edit 2: From the City of Denver's traffic enforcement FAQ: "Depending on the circumstances, officers may request identification from passengers as well." http://www.denvergov.org/police/PoliceDepartment/TrafficEnfo...