Urethane bushings 101

[Doug Rasmussen <76075.2276@domain.elided>]

OK, all you guys putting in urethane bushings, are they REALLY better?  Or
is this more of the "any modification is good" philosophy?

I'm asking this question 'cause several years ago I took a Scout to a
reputable spring shop to have some work done and supplied a new set of
urethane bushing for the guy to install.  He wouldn't install them.  Based
on his 20+ years of spring work, the ONLY bushings he uses are original
equipment rubber type.  And if I didn't like it, I could go elsewhere to
have my spring work done.  

I went ahead and had him do the work with rubber bushings.  I offered to
pay more to install the urethane's so I don't think it was a money issue.  

So, what's the deal with urethane versus rubber?  Not urethane versus worn
out rubber, new urethane versus new rubber.  Why didn't IH use urethane
originally?  Do newer leaf spring vehicles come from the factory with
urethane?

Doug