Seems you can download via bittorrent as well? [1]
BTW, if you download a file of 1.1 GB from boum.org then the size of the download already pretty much gives away that you are downloading tails.. So https does not give you anonymous downloads, it gives you an increased certainty of origin. But as you should verify the signature instead (which is served over https)[2] I think it is fine to download via http.