Ever-curious Roush not looking for exit yet  Jack Roush runs the
largest operation in NASCAR. It's little wonder his relentless
curiosity -- and work ethic -- drives him, writes David Newton.
Updated: March 9, 2007, 12:38 PM ET By David Newton | ESPN.com
MEXICO CITY -- The Busch Series race at the Autodromo Hermanos
Rodriguez was only a few hours away on Sunday and team owner
Jack Roush was going over a manual in the back of Carl Edwards'
hauler.  "When my health diminishes to the point where I'm not
productive, I'll accept a diminished role. I just hope I have my
vision and cognizant powers to make that time interesting as
well." -- Jack Roush  It had nothing to do with road-course
strategy or one of his cars in the field.  It had nothing to do
with racing at all.  This was an instruction book for one of
Roush's newest toys, a Beechcraft Premier jet. He was studying
for a test that he must pass before he flies the plane to future
events such as this weekend's race at Las Vegas Motor Speedway.
"It's 100 kn