Upvote, downvote, accept answer and favorite buttons appear on stackoverflow websites as background images. This limits accessibility of the site: If I view stackoverflow sites in High Contrast display schemes (in my case in Windows 8), these buttons are not displayed. The reason is clear: In order to improve text readability, High Contrast scheme disables all background images.
Is there any valid reason why buttons are kept as background images? Could they be converted to standard foreground graphics?