The justification for getting rid of the link to the Download page under "Get MediaWiki" is that it's already linked from Main Page, which is a point that also covers half the side bar (e.g. the user manual, the communications page, etc.).
This page is the main page newbies on the wiki will want to go after landing on a neat feature they've seen and want to try out, e.g. Extension:DiscussionTools or Extension:VisualEditor. I think it merits being retained on every page.