I never noticed this before, so I think it's important that I make sure others know about this. In an interview with Jeremy Feasel, one of EA's top designers on C&C 4, he mentioned this point.
QUOTE
Q: Is there a population cap? What are the numbers (X/100) seen above the units on the UI?
A: The numbers shown above the units tab indeed represent a population cap. In C&C4, players are limited in the number of units they can make by Command Points, which allows the player to make smart decisions about which units they want to produce depending on the current state of the battlefield and limits single-unit spam and snowballing of attack power.
Ouch.
Click Here for that full interview, as well as discussion on this point..