the only thing that defeats floor coupling is raising your cab a good couple feet or so. i forget exactly how much, but i believe bill fitzmaurice said it was around 27 inches. i don't know all the ins and outs of floor coupling, but a good part of the reason i like to use a tall cab rig or tilt back a smaller one is so i can hear my sound as it's supposed to be and floor coupling doesn't become such a pita.
This is again incorrect (as we've discussed on a number of threads). Raising a cab a few inches (casters, gramma pad, take your pick) will reduce MECHANICAL coupling, which is what causes all the problems on those hollow wooden stage... literally the hollow, resonant space under the floor acting as part of the speaker cab when the cab is literally physically coupled to it. On a concrete floor or other solid floor, a gramma pad or castors will not have any impact on your tone. This is why I always just keep the castors on my cab... no downside, and a bit of upside on a hollow stage or resonant floor.
What you are talking about is ACOUSTIC coupling, and the floor acts just like walls and ceilings, and can impact the tone greatly as you move cabs closer or farther away from walls, floor, whatever (we are talking feet now, not inches). You are correct, pads or castors have virtually no impact on that.
Finally, the reason that you can 'hear yourself' better with a taller cab is not a 'coupling' issue at all. It just gets the more directional midrange a more linear path to your ears, making the cab 'sound' less bassy and more articulate when you stand close to it. There is a bit of downside to this, since the higher frequencies are absorbed by the audience, drapes, carpet, etc. more than the lower frequencies. When you don't have front of house support, you need to crank in much more midrange and high end than 'sounds good' to most up close in order to have an even, articulate tone out in the room. Having that midrange and treble blasting in your ear can result in you setting your tone so that it results in a much darker, woofier tone at front that you realize.