This thread on the Command & Conquer Forums offers additional details from gameplay designer Jeremy Feasel about Command & Conquer 4 in Q&A format. The post was penned a couple of weeks ago, but Command and Conquer DEN highlights a couple of bits that were just added (thanks Ant). Word is:

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.

Q: Does the Crawler gain experience and level up during a match, like a hero?

A: While the Crawler can gain veterancy, just like a unit, all of the experience gained on the battlefield is gained directly by the player, allowing the player to unlock additional units, structures, powers, and upgrades, once the battle is complete.