A semantic paradox in tube terms.

Why is it that military spec tubes made to be very durable and to withstanding extremely violent enviroments. Also said to be built tougher and "quote" more rugged than tubes used in peaceable applications. They turn out to be, in general, to be a better audio tube that simply sound better. They are often a very detailed tube that is also transparent, holographic, crystaline, having a palpably fragile treble.
In effect the workhorses end up sonically in many cases end up as the more delicate sounding variant instead. It makes such tubes a very good deal better sound and longer lasting what more could you want except low priced wich I can tell you again in general they are not.
Take the 7316 sub for a 12AU7 as an example, or the 5751 for 12AX7 or the Jan CHS 6SN7"W". Shouldn't rugged mean thick, tough, heavy,and utilitarian.
Not with tubes.
I can't attribute it to the lack of microphonics which would be the obvious upside of a reinforced structure.
I believe that 7316 and 5751 are not military tubes, but what is referred to as "industrial" tubes, such as the 6922. Though there are Joint Army Navy versions of these numbers, as well.
Some possible factors which come to mind:

-- The fact that environmental specifications (temperature, vibration, etc.) for operational conditions are more extreme than for their commercial counterparts, likely means that in a living room environment tube parameters are likely to fall within a more narrow range.

-- More stringent quality control, meaning that marginal tubes are more likely to be rejected.

-- Tighter manufacturing tolerances.

-- More stringent MTBF (mean time between failure) specs, and more stringent test and/or analysis requirements to verify MTBF, perhaps influence selection of materials so as to reduce burn-in and aging effects.

-- Burn-in requirements during manufacturing test reducing or eliminating the need for burn-in by the consumer.

-- Al