I think I overstated the "exactly" part a bit.  Sorry about that.
Chris is correct in his 
All About Brining section when he says this an estimate; it's not exact.  (Chris, you've got 
everything on this site, don't you!)
That being said, to answer your questions:
 <BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR> 1. Doesn't this mean a lot more brine than would be necessary to cover the bird? I mean, a one gallon bird in a five gallon container requires four gallons of brine to refill to the brim. Do I read this correctly?
 <HR></BLOCKQUOTE>
This technique assumes that the container is not significantly taller than the bird.  If it is, it's not going to work real well.
 <BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR> 2. Did he leave the frozen bird in the sealed plastic wrapper when doing the submerging? This, to me, would not take into account the dead air space in the cavity of the bird. <HR></BLOCKQUOTE>
Yes, he does leave it in the plastic wrap, and you're right, it will leave you a little short.  As I said above, I overstated the "exactly" part.  Again, my apologies.