Very true.
I have not seen any real proof that a cave was involved...
I know that john was old...very,very old....and so I would guess that a cave would not really be where you would expect the people around John and watching out for him would put him to make sure he was doing ok...
The only real clue I see is that the day the revelation started was said to be the "lord's Day....I take to to be talking about the day he would worship with others?...if that is so...then about the last place he would be is alone....in a cave.