The article clearly explained that the granting of compensation was always based on the language of the contract. It had nothing to do with FA or EPL regulations and so would not be limited to internal UK transfers. The same would be true in America. It is true that US sports leagues often have regulations on this, but if they didn't the system would default to -- again -- the language of the contract. The league regulation act as a one-way ratchet. They can limit what clubs demand as compensation, or the situations where it is allowed, but they cannot expand on what would be allowed under general contract law.
Basic contract law requires mutual enforcement. You cannot have a contract where, e.g., Wayne Rooney can demand DCU pay him to the end of a contract even if he gets injured, but if Rooney wants to leave before the contract ends DCU has no rights in return. Employers can never force an employee to stay and keep working. Among other things, it violates the 13th Amendment to the Constitution in the US. And you can't keep a person from taking a completely unrelated job. If Patrick Viera wanted to quit to become a florist, then NYCFC could never under any circumstances stop him or demand compensation. But when an employee working under a fixed term contract quits to get a new job in the same field, the original employer does have rights. There are limits that vary under law depending on the industry, specific job, and such. If a chef is under contract with a restaurant and wants to leave, her employer can probably stop her from working for or opening a new restaurant in the same neighborhood or city or maybe even a few counties away. But they probably couldn't stop her from doing so in another state in another time zone. But the market for soccer players and coaches is international and that fans watch games all over the world means that employers will generally have rights internationally. Leaving the country is not a free ticket that allows you to violate contract terms.
Finally, most people do not work under fixed-time-period contracts, so the employer can fire you at any time and you can quit at any time and neither side has much recourse against the other absent something like discrimination or harassment. All of the above only applies when there is an employment contract for a specific period of time.
And to your last question, the point is to simply enforce the principle that though the big and strong get to do what they want they also have to pay a price. It's natural that both players and coaches will want to move from MLS to bigger, more lucrative opportunities. And the league and its clubs should facilitate that. But they should do so without being chumps that just get stepped on at the whim of big clubs and big stars. Rooney had a contract that protected him for a fixed period of time in case he was injured, or if his skills rapidly deteriorated. Vieira had a contract that protected him against the possibility that NYCFC became unhappy with his performance and wanted to can him. Both could demand to be paid until the contract ended no matter almost anything. The price for that is you cannot leave for a better similar job without offering something back in return besides not being paid after you quit.