1. Spammers aren't going to pay the bandwidth costs to send out sound & video, and nobody is rushing to expand email to carry large files when a URL to a website works better.
Most spam is sent by zombies. So a spammer uploads their spammail *once* with sound and video attachments to a master zombie which seeds it to a few other master zombies in the network which then download it to the other zombies via a bittorrent like protocol. The bandwidth costs are negligible because it's all on the shoulders of the people whose computers got zombified and the recipients.
2.4 statute miles of surgical tubing at Yale U. = 1 I.V.League