Given that xcode is free (as in comes with OS X), why would you get it from a source other than Apple?
The quickest answer is that some countries fsck with the websites of others... I live in China and they love to play games with DNS resolving, temporary and permanent website bans, bandwidth restrictions (sometimes per service... ie just for www, but ssh is full speed).... and etcetera and so forth.
Sometimes you will download from another site just so it doesn't take a week to download, sometimes you don't even realize that you are on a China specific site that is giving you different binaries (ie Skype).
Live within your income, even if you have to borrow to do so. -- Josh Billings