I've found that, in my own experience, those brownout bugaboos relating to program-store-content-loss that trouble the 805x community at large, don't make themselves apparent when the Vcc supply rise and fall times are very short.
probably correct. If the fall time is so short that the period of "who knows what it does" is short enough the likelyhood of 'bugaboos' will be less. Will they be zero, I'm not too sure

Since there are different levels at which various devices perceive "out-of-spec" Vcc, the behaviors of MCU's, supervisors, BBRAM's, and other devices can be very hard to predict as Vcc wanders around the 4.5-volt level. Some devices will respond as though it's a brownout, while others will not.
all arguments for supervisors are based on the selection of a supervisor with the right "activation voltage" if you choose a supervisor with the "activation voltage" of 1V for a 5V system, you will, of course, see no improvement. BTW this is the reason that some circuits can not use the uC's reset output for everytining and thus need an external supervisor

Additionally, I've observed that supervisors do absolutely nothing useful during the power-down transient, aside from activating the RESET. My argument is, once again, that nothing guarantees what happens when RESET is active but Vcc is below the acceptable level.
Well, if you consider satements in the datsheet 'nothing'

While I'm forced by circumstance to respect the general opinion that a supervisor will, in general, make these problems "go away," I know that nobody has made the assertion that they've spent any time testing that notion. Consequntly it's just an unproven hypothesis.
the FDA bases approval on "statistical data" you have the same re this. There are countless posts that after the suggestion of using a supervisor (or in the case of SILabs adding a pullup to the internal super) states "this fixed the problem"

I'm still convinced that the guys at Intel couldn't get their oscillator to start reliably, so they used a RESET time-constant long enough to convince their boss that it would start most of the time, rather than figuring out how to do it properly.
except for "antique collectors" like you I doubt many care about "the guys at Intel" re the '51

The FLASH-corruption issue didn't come about until FLASH-based program store became a reality. This makes the supervisor look more like a fig-leaf rather than a solution. Maybe someone with a real motivation will actually spend the time and resources to perform rigorous testing on the function of the supervisor in this environment rather than allowing it to continue to float in the fog.
repeat/rewording of a statement above, the same answer applies

Erik

PS Ruichard, do you see how easy uit is to follow a post when there is references to what it replies to