The general trend is that TVs have become cheaper and easier to lock down. As hotel guests continue to tinker with their in-room TVs, it is almost in the hotel's best interest to ensure they don't have to send out a technician on a frequent basis unless a TV needs to be replaced. Couple that with the additional revenue stream from selling a movie for $15+ and it is definitely an incentive to lock the TVs down. You can bet that the "only a few occasions" will increase over time.

FWIW, I always bring my iPad loaded with TV shows and movies that I need to catch up on when I have an overnight in the city or on a trip. I have my HDMI connector for it at all times. I've only had three issues in the past 4 years where the TVs did not have HDMI ports (and two of those - Le Parker Meridien in Manhattan and the Atlanta Perimeter Hotel in Sandy Springs - have been remedied either through room remodel/upgrade or hotel remodel/rebrand).