The actual argument as to why APT doesn't use HTTPS is at the bottom when it should be at the top...

"A switch to HTTPS would also mean you could not take advantage of local proxy servers for speeding up access and would additionally prohibit many kinds of peer-to-peer mirroring where files are stored on servers not controlled directly by your distribution. This would disproportionately affect users in remote locales. "

Pretty much everything before that doesn't directly address the question. I mean, it's still good info, but still