I think what you are missing is that aviation should be increasing safety, not reducing it to the minimum margins.
When an engineer does a walk around he looks at aeroplance condition from an engineering perspective - when a pilot does a walk around, he essentially looks at things in terms of "obvious" visibile damage. (Remember the pilot is not trained as an engineer, and chances are he has been given minimal instruction in what to look at for a walkaround anyway).
The next point, where would you rather your pilot be anyway? Preparing up the front for the flight, or in a time compressed rush, running around the outside and then squeezing in all the duties required up front?
I believe the Jetstar turn arounds are fairly minimal - it should take around 10 minutes for an thorough exterior inspection (of course depending on plane size).
Its all about safety - people always talk about the error model in aviation - called the swiss cheese model - now instead of making one of the barriers line up to allow an error to go through unchecked - we are removing the barrier completely!
Anyway - i am sure people have lots of opinions on this.