It's entirely optional, it ensures you have up-to-date documentation, translations (for non-English users) and software listings for the Software Boutique. It's much quicker for @Wimpy to push updates to a dedicated PPA than submitting a request to upstream Ubuntu for approval/uploading.
Of course, new versions will be pushed via normal updates, but not very often.
Sorry, I nearly missed this! I'll note this down and see how Welcome can respect font sizes like the rest of the system.