LOL!!!
I think in the beginning people want another because all the new baby does is lay there.
Once they get mobile and start sleeping through the night is when I wanted another one!! And that's usually when people start wanting again!!
As soon as your baba sleeps through the night, you think "hell, I could do this again!!! this is SIMPLE!!"
But once you get preggers, you realize, oh crap, we're gonna have to go back to square one! And PRAY that your oldest STAYS a good sleeper!! LOL!
Sarah