There's a different use case you're not considering: one-to-many distribution of legal-to-distribute works. I saw a lot of camera test videos from photo forums,

There's a different use case you're not considering: one-to-many distribution of legal-to-distribute works. I saw a lot of camera test videos from photo forums, Android ROMs from Android forums, and PDFs of obscure pamphlets hosted on MegaUpload, because for quite some time it had a less painful captcha/wait process than RapidShare (and MediaFire wasn't popular yet). I wouldn't use MegaUpload to share with my family but I certainly would use it to distribute the 200MB video file I wanted to share with a forum. Most "file sync" and "personal sharing" services try to actively prevent users from burning their bandwidth on one-to-many hosting, both as an anti-piracy measure and as a conscious business model decision. The "share big files with lots of people" niche is useful for people other than pirates, and now that niche is nigh-on impossible to fill in the US.