The problem is that synching audio and video is really quite complex. Video is recorded at a particular frame/second rate and audio at a samples/second rate (each one has lots of different options) and they often don't "divide equally" into each other.
Once you've got your audio and video pieces they have to be "muxed" together. A bit of video, then a bit of audio, then video, audio, etc. Different codecs handle this differently.
And then YouTube takes whatever you send it and re-translates into the format that works with their Flash streaming software.
(Don't you just love standards? I mean, there are so many of them to choose from!) 
In any event, in their FAQ YouTube sez:
The sound is out of sync on my video. How do I fix it?
Out-of-sync sound is usually the result of using an audio codec that our system doesn't support. We're always adding new ones, but if this happens to your video, you can try re-encoding it with a different audio compression. We recommend MP3 audio for best results.
If you've got a piece of software that does a decent job translating to mpeg4 with mp3 audio you're golden. I also had pretty good luck with this last one as a .mov file.
Out of sync vid or not, your performance sounded great. Keep on strummin'!
