iOS 8 Refresh to load desktop site
The desktop site is an entirely different site in many cases than the corresponding mobile website (not including responsive websites, of course).

Because of this, "requesting" a desktop site requires loading a different set of dependencies/resources and a different version of the site you're currently on (this is particularly evident on Stack Exchange sites, but it applies elsewhere as well).

Because of this, the page must reload to re-layout the page and load these new resources, and it would not be possible to do it otherwise, as in these cases it is more than a matter of page scaling.