I'm of the opinion that things like the login form, the registration form, and password recovery should not have other distractions on them and should be designed to keep the user focused on the task. In my observation most of the big players follow this principle. If you go to login to google or change your password there is not other stuff going on on the page. I don't even like menus or navigation on those pages other than a home link in case they change their mind and want to go back to the main part of the site. It also makes it less complicated to secure those pages easily whereas if custom content is added to the page like say images or javascript that don't use relative urls and don't use https (when the page does use https) will cause browser warnings which also confuse the user and reduce task completion/conversion rate.
This is also mentioned in item 2 in this article on smashing magazine:
http://www.smashingmagazine.com/2008/07/04/web-form-design-patterns-sign-up-forms/
So this is how it is by default, but I know other people think differently so I try to accommodate them but in general I try to steer people towards best practices.
Best,
Joe