Not that I plan on sticking up for Johnny, but I wouldn't be so hasty saying that. If you consider your perception as part of the 'system' then the room can indeed effect resolution.

For example, one can not easily separate the direct sound from the reflections if they arrive at the listening position within 20ms of each other. This causes a 'smearing' effect, a loss of resolution, position information etc.. Another example is that long decay rates can overshadow the build up to the next sounds leading edge.

This is not to say that a bad room will stop you hearing the difference in cables (if there are indeed any!). You may find a bad room makes the difference clearer if the cable helps in an area the room deficient in. If your system (due to the room) has a severe bass suck-out, a cable that boosts the bass by +0.5dB may be far more noticeable than if it was in a room that had a flat response.

innit!