Robertson Screws? Drywall Screws?

[NW Modeling List]

The Canadians mentioned these on show 24 <grin>.  I was scratching my head until 
Pierre volunteered the square drive clarification.

Question:  Why these over a Phillips head?  Both would seem to offer the benefit 
of self-centering of the driver, and, on the surface at least, the Phillips 
would seem to have an advantage of a longer lever (the squarehead screws I've 
seen have much shorter bearing surfaces than a Phillips.

What gives?

Another question - why not Drywall screws?  They have an aggressive thread with 
a thin shank, so self thread well.  My intuition is that they would also be less 
likely to strip in soft material due to the deeper threads.  I've typically used 
normal wood screws with pilot holes, especially in areas with a high shear load, 
but I have used drywall screws on occasion.

Thanks

Matt Goodman