Typically, some hosts should ignore the fact that a sitemap item has https support.
For example, the following situation is likely:
Through www.example.org sitemap items that are marked as https should be rendered over https and links to them should be https links
However, acct.example.org that uses the same sitemap, does not have support for https. Hence, marking the 'acct' host to be scheme agnostic is a feature we most support