Isn't there some fancy CSS2 method of doing this?
input[TYPE="submit"] {
// css stuff
}
EDIT: And of course, wonderful Micro$oft IE doesn't understand CSS2. So, include a nice "Get FireFox" button (or just "Get a better browser than the piece of crap you are currently using, if you can detect IE) on your site ๐
EDIT2: Without adding style names to all of your submit buttons, the only other way I could think of doing this would be using Javascript to loop through every HTML element on the page and check if it's a submit button. If so, you can manipulate the style of the object via JS.