I think the addition of the all the differing "strengthening" plates themselves makes not a jot of difference to the integrity of the fasteners, which appears to be where 90% of the cracking occurs; it's the fact the bolts have been removed and retightened to a lower torque which has then removed the compression of the plastic and thereby, the stress, which has made the difference.
Sorry but that is your opinion that is not universal. It may have popular following. My view is torque and the fact that motor stress is carried only by the bottom shell instead of a distributed stress as would carry it better.
But even so regardless of your / others / my view on why - the fact remains that some have cracks WITH plates ... some have cracks WITHOUT ... all valid in my view.
Its your poll - but in creating a poll - it is incumbent on the creator to not try to influence or pass judgements on why / what or where.
It is also a pain but as a creator - you must also accept that some may not agree with the structure or make-up of a poll.
Only being honest. Your poll.
Nigel