As for Bruce, he has mentioned that in the 'old days', they were unwilling to spend the money on a really good monitor system. This has a tremendous impact on a singer (at least some, me included). Now they have the hi-tech monitors, ear plug monitors, etc. So he attributes being better now then before (live) to actually being able to hear himself...
As for head vrs. chest vrs. falsetto - here's a very quick analogy - where people naturally transition from one to the other varies greatly (IMO).
Chest voice - imagine talking to someone, trying to talk in a booming bass voice, like your imitating a giants voice while playing with your kids - 'fee fi fo fum, I smell the blood....' That is chest voice. You can 'feel' the resonation in your chest.
Now raise the pitch to a more normal tone, like talking (or singing) like a normal person, (the giant is shrinking down to a human size) you can feel the resonance switch from your chest to your head (you might feel it in your throat)when you raise the tone. This is head voice.
If the giant kept shrinking down to the size of a mouse, and you continued saying 'fee fi fo fum', you would switch to falsetto to imitate this. In normal speech, falsetto is obvious. When making the switch while singing with power it becomes much less obvious. If you listen carefully to the great ones, you can still tell most of the time. Give Halfords CD Resurrection a listen. He switchs all throughout.
There is one more voice which I am not familiar with, that is even higher then falsetto, but it is something you cannot use to sing or talk in. A Whistle register comes to mind, but I'm not sure.
Personally, after meeting Mark and reading his book, I came to the conclusion that to really improve as a singer - pitch, range, register swithing, etc - you have to dedicate an enormous amount of time to practicing very specific exercises. These exercises make you sound like a dying cat. Very discouraging. Being very limited in time right now, I haven't dedicated that kind of energy yet. If the new Exxplorer CD starts selling, I'll probably start an exersize regime soon to get ready for the new CD.