As a practicing general pediatrician for over 20 years, I can attest to the
fact that sometimes a baby actually does sleep all night very early on.  Even
ones that sleep with adults.  I don't get concerned at all about them as long
as they are growing well and nursing vigorously and often enough through the
day.  The all night sleepers are certainly the exception, rather than the
rule, but some babies do seem to develop a long sleep block early on.  I agree
with post that to have the mom count her blessings.
Linda Shaw MD FAAP