I swear there's something genetic about it; I can see the difference between VHS and 4K clearly every time, but I have to remind and point it out to my wife (she couldn't care about the difference between the VHS-quality rip of a movie and the 4K blu-ray).
It has to be absolutely seamless; the received stopped working and the TV was making the noise instead, and it took a month for me to be finally arsed to go fix it.
We have traditional cable TV, where there are standard def channels on, say, channels 2-99 and then identical HD channels from 702-799, and my wife constantly lands in the SD channels by accident and doesn’t notice the difference. I have switched back and forth between the same show on SD and then HD to show her the huge difference and she just shrugs and legitimately doesn’t see it or care.
I did the A/B test between an OTA broadcast and the cable channel to show people just how poor the cable compression really is. The majority of people could see the difference, but like you mention there's always at least one person claiming to not see it. These are definitely not someone to hire as a QC/QA team member!
It has to be absolutely seamless; the received stopped working and the TV was making the noise instead, and it took a month for me to be finally arsed to go fix it.