There are multiple named projects there that aren't using SSL, and I don't think it's just laziness. If you know of a way for them to use SSL mirrors for no additional cost, I'll work on getting them to switch over.
I suspect that wiki page you linked might be out of date. It seems like all of the Whonix download links on their website are over https, like the VirtualBox images https://www.whonix.org/download/12.0.0.3.2/Whonix-Workstatio....
Whonix also runs a tor mirror, which has significantly more overhead than TLS.
I seem to remember downloading whonix from their site over HTTP around a year ago.
Do you see a tails HTTPS mirror?
For tails: https://tails.thecthulhu.com/. It appears to be the same server behind http://dl.amnesia.boum.org/ based on the TLS cert.
The situation is messy to actually use https for all of these projects, but I think the issue now is organization rather than overhead.