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.
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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.