Not really. You can upload 60 FPS videos, and they are honest to goodness 60 FPS. You might be thinking about <720p qualities, which have half the frame rate of a video (for 60 - 30, for 30-15, and so on). But I doubt anyone is uploading 480p videos nowadays.

Maybe no one's uploading <720p videos, but some people might watch in 480p or lower, for example when on a low bandwidth connection. In that case it's still limited to half the framerate.