It's actually been thought through quite well - if you use a menu command or keyboard shortcut, how is it meant to know which screen you're looking at? For that reason, menu commands and keyboard shortcuts will be applied to the main window, however the right-click will apply to whichever screen you're clicking on.
I understand you have the problem of which screen gets "focused" on using key commands—fair enough. I would have hoped the context of what you were doing would dictate the behaviour. The fact of using the Survey mode means you wish to separate the wheat from the chaff, irrespective of how you got the images to be displayed on your survey screen in the first place. LR seems to think I wanted a combine harvester (cue the Wurzels) instead of a scythe. Perhaps there's some larger utility/flexibility that's heretofore lost on me. Either way, Thanks all for the "solution"—I shall go now employ it rather than argue further for my every whim and perspective to be catered to!