Is there any compelling reason that make update deinstalls first and then
goes to try to build the pkg?

In my naive eyes it would make more sense to:

build
upon completion of build deinstall old package
install new package

The way it currently is done leaves the user with extreme little if the new
package breaks in some way, since he/she will also not have the old software
installed thanks to the friendly deinstall prior to building.

-- 
Jeroen Ruigrok van der Werven <asmodai(at)in-nomine.org> / asmodai
Free Tibet! http://www.savetibet.org/ | http://www.andf.info/
http://www.tendra.org/   | http://www.in-nomine.org/
I dream of Love as Time runs through my hand...