Kraigster414,
No impressive credentials, no master's degree in Metallurgy or Mechanical Engineering, no advanced training in Druidic Alchemy, not a SEAL or Delta sniper, certainly not a Mall Ninja. Never pretended such. Just offered as a personal experience with the Winchester design.
I was shooting a lot of buckshot and slugs, and admit that the wear and tear on that gun was probably far more than most people have on theirs. Factory ammo, gun was well maintained, not shooting 250 rounds of heavy stuff per session. Yada, yada, yada. Went through 6 screws in a year and a half before I resorted to the welding solution and have had no problems since. Still shoot lots of buckshot through it. Just won't personally trust that design for HD use anymore.
Up until that point had never heard of the failure either. Have heard of others since.
When I called Winchester to order the part, they suggested I buy several. That was an insight.
Not alluding to anything, not suggesting it's a systematic problem, meant exactly what I said, ie: I feel that it's just not engineered well enough to stand up to lots of heavy duty use for my needs/wants/trust. As I said, your milage may vary.
I have just as many rounds of buckshot and slugs (probably more) through my 590 now as I had through the Winchester then, and have only experienced a problem with reliable feeding once related to inadequate cleaning on my part. I'll take the 590 for HD use.
As I said, I still enjoy my Winchester shotguns, still use them, and have no problem with the Winchester as a field gun. Won't personally trust the Winchester design for HD use anymore though.
So, no offense taken. Discount it as a freak incident if you like.
As to your 2nd question, Murphy's Law can explain a lot about mechanical failures.