Tell me why

I've never understood why cow equals beef, pig equals pork, but fish equals fish. Oh, and chicken equals chicken. Why do we change the name of some kinds of flesh-based products and not others?

And what about the fact that orange is both a color and a fruit -- And the color of the fruit?! Strawberries are red, but red is not a fruit and strawberry is not a color (except as part of a more precise shade, such as strawberry blonde). Grapes are purple, green, red, white... I doubt anyone has ever said their favorite color was grape.

At first I thought maybe oranges were so special because they were the only fruit of that color, but tangerines, kumquats, grapefruit, and cantaloupe all belong to that color scheme. So do carrots. It seems like a produce family only uses a color as part of a name when it has run out of creativity (I'm looking at you, Mr. and Mrs. Bell Pepper), so oranges certainly have no excuse.