I haven't thought at all about other forms of art but the determining factor as to whether or not some series of minuscule changes in atmospheric pressure constitute music is intent.
If I record a conversation or the sounds of a busy street and present them as documentation, then they are documentation.
If I take that same recording and present it at a concert as a piece of music, then it is a piece of music.
See all the acousmatic stuff that was big in the 60s.
Since this is Slashdot, I guess the "base case" would be John Cage's 4'33". You could argue Cage was presenting nothing at all as music or that he's presenting the otherwise unobserved (i.e. all the little happenings in the concert hall during this piece are in fact the point).
Or, as you argue, it could be said that if you perceive something to be art, it is art.
So, basically, anything CAN be art.
I think resistance easily arises against these notions because there is often the association that art is something worthwhile and people don't always make the distinction between the questions of whether or not something is art and whether or not some art is worthwhile.