You obviously have no idea what your talking about regarding Fender's three screw neck. It is NOT one screw less. Fender three srew system is four MORE screws, two more plates, and two more additional routes than the 4 screw system they were using. There is no way the three crew mounting was thought of as a coast savings. More parts, more labor, and more assembly time can not = lower cost.
Because Fender plans to make the strat for more than a year or two. Newer, cheaper versions of products come out all the time and they are expensive to implement at first, but save the company money in the long run. It isn't cheap for Fender to develop printed circuit board amps but in the long run it ends up saving tons of money compared to hand-wiring everything. When sony comes out with a cheaper version of the ps4 2-3 years into production, it costs money to make it cheaper, but over time they recoup that money. The thinking at the time was that the three bolt neck was going to lead to faster and cheaper assembly. the idea was that it would take less time to set the neck angle than an old four-bolt design. There is also economy of scale in using one less bolt and a slightly smaller neck plate, which adds up when you consider all the guitars and basses fender makes in a year, but i think it was primarily aimed at simplifying assembly.