Plenty of people buy cars and don't do maintenance beyond oil changes/air filters simply because they don't have to during their ownership of the vehicle. Not every owner is doing plugs every 30-50K miles, and when that happens they can become seized, not every car has plugs that just fall right out when you open the tool box. Look here, plenty of threads about seized plugs around, but luckily very few or no threads about broken ones. Toyota uses a tough alloy for the heads and the OE plugs are not prone to breaking off even under high torque.
And yes, there are in fact spark plugs that will last and maintain performance for 100,000 miles. Denso currently has a spark plug with an iridium center and platinum ground, I've pulled a few examples out of newer Corolla that have 100,000 miles and the gap has barely changed from that of the new plugs, the only wear appears to be sound rounding and very very minor recession of the platinum ground point. I believe Bosch (and maybe Bosch sold as Motorcraft) also have similar spark plugs out now as well. Extended service intervals are a big seller in the new car market because cars are ranked and rated by various media outlets on their maintenance costs so the farther down the line you kick that can the better your car looks. More and more life time fluids, 100,000 mile coolant, 100,000 mile spark plugs, life time timing chains, etc etc. Lots of marketing wank but those Denso plugs really do go the distance. And they've been made available in M14 thread now for a few years, I have a set on my 2ZZ.
