Good luck on getting 100% firmware updates. Ain't gonna happen.
Back in the olden days when 8-bit processors roamed the Earth and programmers carefully coded assembly language programs to fit in a 2708 EPROM with pride in their optimization, I would agree with you.
These days however, the crap that they call embedded firmware is more times than not a virtual disk image of a Linux (or other RTOS) filesystem stored as a file on a bigger flash partition. The bootloader can run checksums against the disk image, and only load a sane image. If there's a bug, the bootloader can sense that the new image failed to execute properly and fall back to the last working image that is still stored on flash. Not saying that any process will be 100%, but five 9's is not unrealistic from my own experience. The chance for firmware bugs and errors is much greater and the QC much lower in this distribution model, that's for sure.
Just looking around my house, TiVo sends quarterly updates to my DVR. Samsung has already sent a few firmware bundles to my TV for new streaming features. My smart phone has received at least 7 forced/automatic over-the-air major firmware updates in the three years that I've owned it. Even my home router receives pushed automatic updates. If any of these vendors were worried about "bricking" a significant number of customer devices, they surely would think twice before pushing out updates.
FWIW, I'm not part of the beta, so I can't comment on AcuRite's implementation.....