Look who's NOT talking

I apologize for the bad movie title reference. But in true first-time mom fashion I have been staying up some nights wondering (worrying) why my now 14-month old hasn't said a word yet. I mean he does speak all the time - just not English. I've turned to other mothers, ones with a bit more experience and they all say the same thing - nothing to worry about, he'll talk when he's ready.
During these times of self-torture, I argue that he does know what I'm saying. I can ask him to get his milk or water and he knows the difference. He knows what his choo-choo (soother) is, will grab snoopy if asked, has his own special sound for Crash (our cat) and waves bye-bye.
It's when I see other kids his age saying things. Like the little genius Olivia in his daycare room who points at my son and says "baby". Yes, I say to this little know-it-all, it looks like he still is a baby since he can't talk yet and you can and you're one week younger than he is.

Why do we do it? Why do we attach any meaning to how fast or slow our kids develop? Why do we take some sort of credit when they do something faster than other kids (Deaglan walked at 9 months!!) and take it personally when they aren't as far along (Deaglan still doesn't sleep through the night)??