Is it wrong of me to want a cheeseburger?

Not at all.  Come to think of it, I could go for one too.

Only if part of the very same cow that gave the milk for the cheese is also now laying on the bun.

Perfectly natural, if you're a cat. http://icanhas.cheezburger.com/ (Check out those meowls!)

??  Milk comes from cows, meat comes from steers. Apparently you never watched a cowboy movie.

Either you're joking or you've completely unfamiliar with cattle husbandry.

First of all there are some breeds of cattle raised for meat, like the Polled Hereford, Black Angus and Texas Longhorn (yes, some ranchers are starting to seriously breed them again.) Trust me, you've never bought milk from any of the "meat" breeds at the local supermarket. Those cows never see the inside of a milking parlor, only the chute at the slaughter house like the steers and occasional bull.

And as to those bred for milk production like Holstein (yeech!) or Brown Swiss or Guernsey . . . what do you think happens to those old cows when they go "dry"? I remember "ole' Suzie" being served up all winter long after she went dry many years ago. Most of the young dairy bulls are castrated (turned into steers) and spend a very short life being raised to become veal.