Old & New "Studio" equipment

Always the deal slut, I've been noticing on ebay, etc, equipment like (old) JBL Studio monitors & amps like Hafler 9000 stuff - stuff originally sold to studio pros.
What do "they" do, that "we (audiophiles)" dont do, (and visa versa)?
How does "studio" equipment sound different?

(posting similar but speaker specific question on speaker area)
BTW, one thing I _have_ noticed, on both Bryston "Pro" equipment and JBL "Studio Monitors", is that they are gain or sonically tweakable. The Bryston stuff has L&Rgain controls on the amps, and the JBLs have mid & hi controls on their fronts.
Just keep in mind that some pro gear will only take XLR/DIN plugs..