Everybody considers art different. For me games are art because it's extremely difficult to bring a made up world to life with music, artist, characters and good gameplay. I don't consider paintings like this http://1.bp.blogspot.com/-nN4X_z40N0U/T0D-DZIdEkI/AAAAAAAACSk/2gJtrX4SAdU/s1600/Pollock_no-5.jpg as art because boring people see things that aren't there. (FACT: this is the most expensive painting ever).
It was until last week when Picasso's Le Reve ($155 million) surpassed it. (Not sure how currency and inflation rates effect it so could be tricky to state it admittedly).
I agree on your point though, art is what we say it is. Games to me are a form of art on par with literature and film. I think this mentality comes from an older generation that either is ignorant of the medium or still pictures pong and pac-man when they hear video games.