A significant portion of the population finds it completely acceptable to plaster their political beliefs on their bumper, both via stickers or their license plate itself. You might find it distasteful, but it's hardly rare.
Isn't going through great lengths to cover the logo up only adding to their brand identity? It means you attribute so much value to it that you need to contrast it to one's (or 'your') own identity. I don't have a strong emotional reaction to the Apple brand and just like my macbook to be clean and professional.
I tend to like them clean myself. But in an office with a very large bunch of identical machines, stickers kind of become a standard way of making your own laptop easy to identify.
