RVDT:
I am not saying that this particular issue is relevant to the accident in question but if you apply the intent to many aircraft and realise that the loss of ONE attachment is enough to bring the aircraft down and yet the fastener is not locked this way and sometimes if at all. Additionally there is no way of telling if it is in fact locked. There are numerous aircraft out there where the intent of this part of the FAR is NOT complied with or may be under an AMC - (Acceptable Means of Compliance) which in some cases is proprietary and is difficult to get verification of.
I'd be interested to know which fasteners you've seen which are not locked per the FAR requirements. If on your preflights you ever spot a non-locked fastener please let your engineers/mechanics know asap.
However, you may be looking at a self-locking nut and just not realize it. For example, a fiber or plastic insert self-locking nut is easy to spot, as is safety wire. However, many MS nuts are self locking through a "crimping" the metal which runs down on the stud or bolt. Once the nut is secured on the bolt/stud, there is no obvious "locking" device to see. But these nuts are indeed self-locking, they just may not look like it.
Someone earlier on this thread talked about how the nuts on the filter housing studs might have been run down finger tight. Not likely...from the photo of the transmission filter earlier on they looked like self-locking MS nuts to me and I can assure you they require a wrench to run them on to a stud or bolt.