This reminds of" Class A" materials or parts specified for use in nuclear plants by the Nuclear Regulatory Commission. "Class A" stock simply meant that the supplier certified certain parts for use in nuclear applications. The screws, nuts and bolts and other hardware or parts were no different than what we were buying for non Nuclear plants, they were just certified to meet the spec. They class A designation meant we had to pay twice as much as the non class A. There was no difference in the hardware and it was supplied from the same vendor.
It's almost exactly the same concept. MIL-SPEC materials are the exact same thing as the exact same part without the MIL-SPEC designation. Example, if the specific alloy used to create this: DEWALT 20 oz. Hammer-DWHT51054 - The Home Depot is used in any single product that the military uses, then this hammer can be called "MIL-SPEC" or "military grade". It doesn't mean the military uses that hammer, or one like it or anything similar to that. It simply means that some or all of the materials are in common with military products. The only reason the SPEC exists is so that they can make sure they're getting the same thing over and over, for the interchangeability of components.
Now for those who served... does the military buy top of the line products for every single product they purchase? Or do they sometimes buy things a little cheaper than the highest quality item available?
The 810G rating is different from the above in that it is an actual standard, but the conditions are so loose that most products, including most electronic products, don't bother with it - because it's an absolutely meaningless concept for most consumer goods.