If you wanted a simple change that was general purpose such as Submit, you would just change this in the resx file. The difficulty comes when trying to use logic in the code to reach the resource file for one of the two options. (not that this is difficult, just adds another possible point you can screw up)
The reason nothing like this is handled with image buttons anymore is because of localization. You could, yes, use a css attribute if we changed the code a bit, but this would defeat the purpose of localization.