I'll bet they do, since I don't actually know anyone who doesn't re-encode their videos. Youtube certainly does, Vimeo does (at least some versions, since they offer different qualities) though uploaders have the option of offering the original for download.
Re-encoding is generally always done, since users upload so many different formats, and few of them are suitable for streaming.
Re-encoding is generally always done, since users upload so many different formats, and few of them are suitable for streaming.