These are not myths, these are facts. Any time you have a case failure you run the risk of a catastrophic failure to the gun.Again, this is incorrect. A case failure will send gases down the mag well and usually blow the mag out. If any damage is done, it is usually to the mag and mag catch.
A catastrophic failure would be one in which the barrel is split, frame is damage and the pistol is ruined. These have happened to any number of different pistols, H&K, Glock, Ruger... These are always the result of severely over pressured ammo.
Proof of this can be seen in the FACT that H&K pistol have much better supported chambers than do Glocks. And yet they have still had major KB's in them.
It is the ammo, not the pistol.
You are correct that these types of failure can occur in all types of firearms Unfortunately not all failures can be attributed to ammo alone! There are a number of reasons for a pistol to have a catastrophic failure, such as pulling the trigger when the barrel is clogged, over-charged cartridge, under-charged cartridge, weak brass, metallurgic failure, insufficiently supported case etc.
I will disagree with you about the results of a case head rupture. The light damage you suggest can and does occur but other damage can occur as well. some of the damage done by the rupture of a case can be blow the magazine out of the gun, damage to the locking block or engagement surfaces, damage the trigger, ruin the trigger bar, rupture the barrel, peel the forward edge of the slide at the ejection port up, and do other nasty things. In general, glocks tend to contain case failures fairly well, but under some circumstances they can cause injury as well as damage to one's gun. I for one would prefer a better supported case as opposed to a lesser supported one.
The following statements can be found in Accurate Arms' current reloading guide regarding .40 S&W pistols and supported/unsupported cases:
"In recent years it has become very apparent that there exists a situation regarding some pistols chambered for the .40 S&W cartridge. Some of the pistols currently available to shooters may not provide complete support to the case when a cartridge is chambered."
"This information [AA's load data] is safe for use in firearms which provide complete support of the case. Failure to fully support the case with cartridges of such intensity may result in bulged cases, ruptured cases, separated case heads or other consequences which may result in damage to the firearm and/or injury or death to the shooter and/or bystanders."
"If you own a firearm chambered for the .40 S&W, we recommend you contact the manufacturer to determine if the case is fully supported."
"If your firearm does not provide complete support for the case, DO NOT USE Accurate Arms Company data or products to reload your .40S&W ammunition."
"This is the first time Accurate Arms Company has felt it necessary to place such a restriction on the use of our products, but the continued safety and welfare of the shooting public compels us to do so."
NOTE THIS IS NOT DIRECTED TOWARD GLOCK(my statement) I feel that you might be perceiving this as a blanket attack on the glock, it is not intended to be, I just have some reservations about some design decisions that they made earlier on in their .45 and .40 cal line. As I have stated before I believe they have corrected the situation in current production. This kind of occurrence can and has happened to other companies. I also feel that glock could have handled it in a better way but they were probably doing it the way their lawyers told them to.