Any kind of manufactured glass product like this has the potential for a manufacturing defect to suddenly spring up. Any time glass is worked, there are stresses involved. And glass is really more of a very, extremely, slow moving liquid anyway. It can change a bit in shape over time - and if it was stressed or defective in some way, I could see how it would crack. Car windows, being tempered, are laminated with plastic and somesuch - and a tiny crack or break can spread very quickly. Especially something like a windsheild that is glued in all around, and if the metal of the car deforms somehow, or is putting pressure on it, the crack would expand as well. Picture tubes are full of vacuum (or is that not full of it...
). Lots of pressure is trying to crush the tube from the outside. One little crack in the right spot and *FOOMP!*.
Modern tubes have the "integral implosion protection" which is just a tensioned rimband around the outside, to crush the tube in on itself if it breaks. Old tubes, without this, lived behind glass, just in case.
One thing I've wondered - is on the 21FJP22, with the bonded safety glass, what happens if it implodes and the glass has been de-glued due to cataracts and taped back on? It should provide protection, but will it stop glass from flying everywhere?
But, all that aside, these things really have a one in a million chance of spontaneously imploding if they're not abused/kicked/dropped.
But still. The set came with a very durable glass in front of it, and I think that leaving it there is a good idea - but I wouldn't lie awake at night if it were missing. Any spontaneously occurring crack is most likely to happen at the weakest area of the tube AFAIK. That would be the neck or stem. And such failure would be just a hiss as the vacuum escaped. Nothing spectacular.
I've never had a tube implode unexpectedly. I've had some tubes unexpectedly NOT implode though - modern tubes at least are very tough. When throwing away some dud modern tubes, even chucking it into a dumpster won't always break it (the face and sides are very thick).
-Ian