It keeps record of it. Unfortunately, it's only on your computer (and you can actually edit the file manually, if it makes you feel better). You can spend your time collecting them for your own pleasure like on the other systems, but you can't really show them off - Not that anyone cares too much.
Of course, achievments on the systems you mention don't actually do anything, either. They just give you "points" that demonstrate how much time you've spent playing the game ...and how susceptible you are to getting an addiction.
In summary, they're just for fun.
