If this is what I think it is, not being able to stop automatic
reading of live regions sounds like a serious deficiency. I believe
there are sites, such as financial sites, where a stock ticker might
be a live region. How can you work well with a site of that sort if
the live region is constantly trying to speak as information changes?
Does JAWS have a feature to stop automatic reading of live regions and
am I correct about what they do and that this may be a serious problem
on some sites?

Having said that, if the original poster doesn't use such sites, and I
suspect the majority of people don't, and if the only problem is the
youtube problem, I still consider that to be an absurd reason to
prefer one screen-reader over another.
Gene