Also..what technique are they using for image replacement for the headings?
#pageHeader h1 span {
display:none
}
Personally, I prefer the “offleft” technique, because display:none will make the text invisible to screen readers.
They all use background-color:transparent;…..why? is this to cover up for older browsers?
The default value of the background-color property is transparent, so this is redundant. As far as I know this will not give you any problem in older web browsers.