I think a lot of consumers buy D M*gs and become a little frustrated when they try to buy a replacement bulb from the place they bought the original flashlight. That is why I think I've never heard anyone recommend going to Wally World to get a bulb. I'm sure some stores somewhere have the correct bulb but, in general, they are low on stock so the correct bulb is usually not available.
So, the end-cap replacement is used. Maybe it is just paranoia ("It is not paranoia if they are all after you") but it seems like the end-cap replacement bulb is designed to fail when you most need it.
On M!n!-M*gs, mine are all now powered by BBs and MMs. When I had rice-seed incan bulbs this is how I blew them: If I needed a light for a nocturnal adventure to the terlot, I enjoyed reaching for one on the night stand and knocking it over to hear it roll along and fall two feet to a carpted floor and just know the bulb had blown. It really pissed me off which was OK in that scenario. Later, I would replace the bulb with, of course, the end cap replacement.
If I had a rough day the following week I used to like to come home and stare real hard at the M!n!-M*g with it's 'good' replacement bulb. I would just focus my eyes on it and could blow up the bulb. I tried this technique on other equally irritating objects and, admittedly, a very few people but it only worked on a M!n!-M*g.