TL;DR?
Today he has a big fan club, runs some airfare-hacker forums and gives interviews to magazines with no journalistic credibility or fact-checking whatsoever (cough cough). Airfare hacking today is harder than it used to be, and you can't even defraud the US Mint by ordering dollar coins on your credit card (with no fee / free shipping), but you can still get lucky with mistake fares and/or pay people to violate all the terms and conditions and fly in your name, if you're sneaky about it.
Guy should use his brains for something more useful, like solving the traveling salesman problem.
In terms that you can understand: legal != right
Engaging in human hacking and systems analysis of institutions like this can have high personal pay-offs, but it also often requires to revolve much of your lifestyle around it, so whether it's worthwhile varies.
He also writes a blog about it.
wouldn't removing this simple feature nullify what he's doing or at least a great deal of what he's able to accomplish?
Typically what Ben is doing is flying fares where the cost of the fare is lower than the equivalent value in miles, or where he can game the very complex rules associated with a frequent flyer ticket to add on a free leg or free flight.
So, for example, for my honeymooon I was able to snag round-trip tickets in business class from NYC to the Maldives. Once I had those tickets, I worked the frequent flyer system to move the dates around and add on a stop in Tokyo in First class for a couple of days for about $10 in extra taxes and fees - total retail cost of the tickets was close to $30k, our total cost was <$250. In terms of frequent flyer mojo, this doesn't even count as journeyman-level skills.
On top of that you have all of the points he's getting for using various branded credit cards, maximizing bonuses, giveaway offers, etc.
The only way I'm aware of to get FF points when you are flying on an award flight is when you get hit with IRROPS (irregular operations, usually due to weather and mechanical issues), and at the airport they rebook your award ticket to be a revenue ticket at no cost. It's something the airlines have discouraged their agents to do for obvious reasons, and they've tried to make it easier to rebook award tickets, but still if you're a top-tier elite, there's 50 people that need rebooking behind you, and you're on an award ticket, decent chance the computer will spit out a revenue ticket to replace the award ticket that is no longer valid.
No, that's typically not how it works.
From an incentive point of view it makes sense, otherwise, spending all your miles would be an opportunity to jump to another airline.
This particular abuse seems like an extreme case, and really, what is giving a seat to one guy who goes to extreme length compared to the returns on the general customer base?
By invoking certain rules or offers, you can actually get many more reward miles than the actual distance of the flight. That's why a large part of the practice is spending as much time in the air as possible.
Using those near-currency credits to bribe the airline employees with the airline's own stuff is likely another key part of the "fly free" strategy. The employees have some discretion in how strictly they enforce their employers' rules. Make friends there, and you have an easy flight. Make enemies, and you will have trouble.
There has to be some mechanism that makes this works for them, otherwise they wouldn't be doing it.
This article reminds me of one I read wherein a Chinese man bought a first class ticket for gratis access to the airport lounge, ate there for free, and re-booked his ticket for another day. Months worth of meals for the cost of one fully refundable first class fare, and he never explicitly broke a single airline rule.
This is just extreme couponing. This is the airline equivalent of walking into the checkout at your local grocery store with 3 carts full of stuff, and walking out after getting change back from your nickel.
Not just frequent flyer miles (which you generally can't get on flights you get by redeeming such miles), but credit vouchers, etc. (that's the whole point of the analysis of which fights are likely to be oversold, so you get tickets on them -- perhaps with frequent flyer miles -- so you get to fly on a later flight after accepting the offered voucher reward for being bumped.)