Auto vs Aircraft registration aren't 100% analogous in every aspect, but in some senses, yes. If someone else has that plate, it's theirs. I can't just tell Mr. Government to take it away from them and give it to me simply because I want it. They're doing nothing wrong by simply having it. It doesn't harm me in any way. Nor does it affect my ability to register my aircraft.
We're not talking about *after* it's affixed to a car or plane...then they *would* be analagous, because I can ask someone with a car with license plate N12345 if they'd take $X to turn it in so I can have it (I assume DMV has a way to transfer a plate from one car to another, I dunno), same as I can do with registration N12345 assigned to an aircraft.
The disparity happens here *before* then...while the government (state for autos, federal for aircraft) retains control over the "license plate numbers", including "vanity" plates. Automotive, you can't get a vanity plate unless you have a car to put it on, so there's no real ooportunity for someone to turn a government (taxpayer-funded) resource into something akin to a monopoly. Aircraft, you can get as many vanity plates as you want, without a single aircraft to attach them to, thereby allowing someone to theoretically acquire as many "plates", vanity or non-, as they wish and charge any price they wish.
You can argue that it's legal, therefore it's okay. I tend to think that when the FAA created the system whereby one could request specific N-numbers, they intended it for use just as most of us here are using it...to get an N-number that is meaningful for your private plane, or business aircraft. I doubt they intended it to be monopolized by a guy who does nothing more than turn around and charge ridiculously high fees while running some sort of sperm bank.
Cybersquatting, patent trolls, this guy...all in the same category, as far as I'm concerned. Seems a simple change to the regulations would end this bit of abuse.