I have seen touring cyclists on I-80 in WY and read a lot of logs from others who've cycled a variety of different Interstates - usually legally, sometimes not. In WY, there are bike signs (not many, but I saw a few) both on the Interstate and on-ramps through the section where bikes are allowed.
That said, it's not unusual for police to be unaware bikes are allowed on some sections of Interstate. It's more understandable in light of the fact that cyclists really are banned from riding most Interstates - just not all of them.
When it comes to the idea of cycling on the Interstate, doing so makes good, safe sense to me, but only so long as we're talking a section without lots of on/off ramps - say, deep in the middle of nowhere in WY, NM or any number of other predominantly Western states.
Yes, you're cycling on a road where traffic is moving at 80+mph. You also have a full lane-width shoulder to let you be separate from the cars. This seems safer to me than cycling a 1/4 lane-width shoulder with 45+mph traffic, much less a shoulder-less road with that traffic speed. The dangerous part is crossing on/off ramps where you have no choice but to mingle with the high-speed traffic.
While I wouldn't seek out Interstates to cycle on, I can definitely see doing it. Indeed, the idea of cycling local non-urban Interstates scares me a whole lot less than does the thought of getting over the shoulder-free 2-lane 45mph feeder roads I'd have to use to reach the Interstate from where I live.
I'll also be the first to admit that whether it's legal or not, cycling on the Interstate is one of those subjects where the 'right' answer will vary wildly depending on who you ask Aside from the question of legality, this boils down to personal preference and perception of the source of the danger.
I see the difference in my speed vs. traffic speed as less important safety-wise than my ability to physically separate myself from the stream of higher-speed traffic. Others will, no-doubt, perceive much different safety priorities. Who is right? Depends on the specific situation.