@whooami: ;) explanation: the way I upgrade is via ftp I just select all files in my root, move them to a temp directory and then upload new files. That way I can easily delete old files and copy back old files (and database) if there is a problem. If no problem, then I delete that temp directory, with the robots.txt inside...
I agree it's super simple to create, upload, and maintain the file, but the addition of the file with the core files will help to educate all users--robots.txt is such an important/intrinsic part of creating any website/blog that it is amazing that so very many people do not understand/use it. I know it's a pain in the arse to support it, but it's one more step for the developers to truly make WP a universal product.
If the blog is not stored in the root, then the file will just be ignored anyway. However, if it is in the root, robots.txt can help defray potential server hits from certain bots ,and therefore have the server running a bit better.