This is what our professor said:
As a matter of fact, NAND and NOT(invertor) are fundamental to LSI.
Such qualities of NAND as speed or power consumption depend on NMOS. Those makers who can provide excellent NMOS are at present only five – Intel, TSMC, Samsung, Toshiba and Texas Inc., among over 1000 CMOS makers.
The five can produce LSI only with NAND and NOT. Others need NOR, which are not effected much by NMOS’ quality.
“This textbook,” he said, “explains first NOR and then analogically NAND, because the writer of it have been working in other maker than the five.”
Especially Intel has a special technlogy to produce LSI mostly with high-speed NMOS and few pMOS, called “dynamic circuit”.
And he said again to the student, “You have to thank for those people, who let you enjoy Playstation.”