I remember how pissed I was in 1998 when I tried to register my first website and found most names were squatted already. Truth be told, I'm still bitter at domain squatters.
"Thank you for your interest. The web site is under extensive development and is not for sale. Only a (1) public company or (2) private company with sales in excess of $5B would be considered."
First of all, that website looks the same now as it did 10 years ago. So I'm not sure what "extensive development" means. And second of all, why would it be any of his concern whether my company is public or makes $5B in sales?
That really rubbed me the wrong way. I'd rather just get back a ridiculous number that I'm obviously not going to pay.
If he did what you suggest and replied to everyone with a ridiculous price -- "Hi, USD 20 million, ok?" -- then he'd just get a second wave of emails from people trying to haggle:
"That's outrageous! The domain is worth $100k maximum. I'll pay you $2k and give you 0.1% equity in my awesome startup. Deal?"
And if he doesn't reply to that, then the person will send another email with the worthless offer slightly tweaked, and so on... So he's better off setting a precondition that prevents the pointless replies, basically "I'll talk to you only if you have a legal department with more than 20 people."
Anyway, good luck to him. I hope when he is ready to sell his domain there is someone looking to buy it for the kind of money he's expecting.
Every era has its own opportunities. You should look around for stuff that's happening now, instead of looking back to what you might have done in 1993.
With a short domain name, the owners waste the short name for the cheap price of domain registration ($20 max?).
The problem with the idea of charging parked domains is that defining what is "parked" is hard, and can easily be gamed.