The latter is not true. Airlines' contracts of carriage prohibit "Point Beyond Ticketing." Here is what (e.g.) United's contract of carriage says:
> Fares apply for travel only between the points for which they are published. Tickets may not be purchased and used at fare(s) from an initial departure point on the Ticket which is before the Passenger’s actual point of origin of travel, or to a more distant point(s) than the Passenger’s actual destination being traveled even when the purchase and use of such Tickets would produce a lower fare. This practice is known as “Hidden Cities Ticketing” or “Point Beyond Ticketing” and is prohibited by UA.
And violation of this provision can, in fact, have repercussions:
> UA’s Remedies for Violation(s) of Rules - Where a Ticket is purchased and used in violation of the law, these rules or any fare rule (including Hidden Cities Ticketing, Point Beyond Ticketing, Throwaway Ticketing, or Back-to-Back Ticketing), UA has the right in its sole discretion to take all actions permitted by law, including but not limited to, the following:
> 1) Invalidate the Ticket(s);
> 2) Cancel any remaining portion of the Passenger’s itinerary;
> 3) Confiscate any unused Flight Coupons;
> 4) Refuse to board the Passenger and to carry the Passenger’s baggage, unless the difference between the fare paid and the fare for transportation used is collected prior to boarding;
> 5) Assess the Passenger for the actual value of the Ticket which shall be the difference between the lowest fare applicable to the Passenger’s actual itinerary and the fare actually paid;
> 6) Delete miles in the Passenger’s frequent flyer account (UA’s MileagePlus Program), revoke the Passenger’s Elite status, if any, in the MileagePlus Program, terminate the Passenger’s participation in the MileagePlus Program, or take any other action permitted by the MileagePlus Program Rules in UA’s “MileagePlus Rules;” and
> 7) Take legal action with respect to the Passenger.