Typical vs. min/max timing and voltages
Vcc typical 5V (with a minimum and maximum of 2V and 7V) ... why use Vcc = 2, 4.5, and 7 volts as its conditions

Probably because the characteristics at 4.5 V are less desirable than those at 5 V.  If they specified values at 5 V, then you couldn't use them with a typical "5 V" supply that could be a little below 5 V.  They are specifying the characteristics for a slightly worse case than 5 V so that your supply can have a little slop but you can still rely on those specs.

time the pulse needs to be active ... minimum 16 ns ... typical period 5 ns

There is nothing inconsistent here.  The minimum is the real spec.  You have to hold the value for 16 ns if you want it to be interpreted correctly all the time.  It usually takes only 5 ns, but you can't count on that.