YouTube is generally NOT better quality.
YouTube is only 192 kbps IF the video is HD. On SD videos it's at most 128 kbps. Music is rarely uploaded in HD, especially if it's a static picture or fan made video rather than an official video.
Also, and this is the big one, most YouTube videos are transcoded. They take whatever audio stream is on the video when it's uploaded and recompress it. Trancoding is one of the worst things you can do for sound quality.
Maybe your YouTube videos, if you upload in HD without transcoding, are high quality, but the vast majority of YouTube videos are not.
1. Yes it is, YouTube is 192 kbps AAC in HD, even in SD it's still 128 kbps
AAC, beating Soundcloud that is 128 kbps
MP3. AAC 128 kbps compares favorably to 128 kbps MP3.
2. Pretty much all channels I watch (EDM music mostly) upload HD 720p+ (I would be disappointed to find a non-HD channel these days) but then again I only listen to new electronic music.
3. Not worse than Soundcloud which transcodes or recompresses into 128 kbps MP3 for playback. (Source, point 1: http://help.soundcloud.com/customer/portal/topics/109407-uploading-transcoding/articles)
4. You can find HD quality for most music today, at least on some channels. Maybe if you're into older and less popular music it could be harder but majority of people listen to popular music.
Let's take an example:
https://soundcloud.com/datweekaz/da-tweekaz-ft-anklebreaker
vs
http://www.youtube.com/watch?v=Js97DYVuNmc&hd=1
Having said all that, I still want to see soundcloud embedding on head-fi.
But don't try to argue with soundcloud vs youtube quality, it's pointless. On the other hand Soundcloud is pretty convenient to use/listen through, less bandwidth is wasted and you can upload stuff faster as you only need the audio file.