I'm going to differ with McLuhan in a know nothing sort of way (if that's what I'm doing) and say the media isn't an art form by itself. Otherwise, I guess I could go to my hardware store and call their paint rack the "art gallery". Of course that's foolish... so there's more to it than that. If that's what jtk means, fine. Otherwise, did someone say "harsh"?
Watercolors, pastels and charcoal are their own medium and because they're "soft" require different handling, framing, etc. Often they're not shown with the others but separately. Do I want to go look at charcoals? Um.... fairly, I find sketches less appealing unless I get to see the sketches near the actual art works they were often part of.
Similarly, I will say that... for many years (load your arrows now), I didn't think of B&W photography as art per se and with color photography it was just pretty pictures. I was a neanderthal, and found that part of an art gallery.... challenging. Discovery through participation has changed my view and today I look at it differently, and realize the skills involved... though my own perspective is that I'm not sure how to look at digital and whether the artist is a collage specialist, special effects artist, programmer, or what. Many images are amazing, but maybe photography is only the starting point. So it's a new medium. Film photography... is and isn't the same. Audrey Bodine was "photoshopping" Caribbean skies into his Chesapeake Bay photographs back in his darkroom in the 1930's.
Galleries will do what they want. Artists will as well. Have fun.