My experience is that most breastfeeding newborns do not pee very much the first day, are wetter the second day, and by day three to day four are voiding almost as many times as they eat.  If they aren't its a signal to question mom's supply, check the latch, etc., etc...

In the hospital moms, especially primigravidas and their partners, tend to change the baby very frequently -- in part because they are so excited by this new wonder and every time he cries or fusses or they pick him up or put him down, they check the diaper.  And then they have to change it whether it's wet or not, because our hospital disposable diapers don't "stick" the second time.

I think after  the baby is a few days old, they have gotten disenchanted with changing diapers, and don't check quite so frequently.  And unless there is NOTICEABLE wetness (or a messy diaper), they don't feel the need to change it, because these are absorbent, right?  So baby might not get changed until the diaper is sopping wet from a collection of pees.  And then, of course, they think the baby is peeing copious amounts because they have one or two soaking diapers a day.

BTW, I am very vocal about my disapproval of disposable diapers, as I teach parents how to clean their precious' bottoms.  I do let them know this my own personal opinion, but...and go on to talk about the cost to the baby's bottom, the economic cost, the ecologic cost, and the practical necessity then to have a dozen or so cut up towels or washcloths, anyway, for washing baby's bottoms, wiping up spit-up and dribbling, protecting one's clothing, and so on.

Sincerely,  

Chanita, San Francisco