I have for years tried to set an example of uploading mods to multiple locations and using file mirror sites as well. Even created a http://wiki.tesnexus.com/index.php/List_of_online_hosting_sites to describe the free resources available to everyone.
It is not an issue of how great a site is, its about putting all your eggs in a single basket and how that is never a good idea. But many people just don't care or think the mod is worth the effort and figure if the site goes away, so will the mod.
I cannot speak about the variance in download speeds since I don't watch it that closely. It comes down fast and I simply don't hang around to watch. I typically spend most of my downloading time prepping the last archive I downloaded by adjusting the file structure, readme details such as adding a readme if one does not exist and recording key details such as date it was modified, version number, author, download URL and permission info. That keeps me fairly busy doing that more than waiting on downloads to finish downloading.
EDIT: TESSource.net was/is TESNexus. When Dark0ne broke ties with his partner, he retained the forum data and the mod database but had to re-write all the code which is now TESNexus. We also lost all images attached to the mods and with help from the community, much of the old mod images have been restored.
Also, PES does have a 25MB file cap but that is ONLY with the automated upload page. They have an FTP site you can upload larger files to and then send an email to them letting them know which file you uploaded and to which mod page it should be attached to. That is what I did with Lost Paladins of the Divines way back in the day and the process is still the same today.
LHammonds