curlyLJ, anecdotally, my friends who FF their babies find their babies sleep for longer stretches at night than friends who BF their babies.
Add to that the number of BF-ers I know, and know about, who do a bedtime formula feed, specifically to get the baby to sleep longer, and I'd say yes, it seems like formula often (obviously not always) does = more sleep.
And I've assumed this is down to the artificial feeling of fullness formula gives a baby, and the longer time it takes to digest.
Of course, the BIG sleep issue with BF-ing is that you can't share feeding duties, unlike FF-ing. Only the mum with the boobs can do it - so yes, if you have a new baby that feeds every 2-3 hours or so (or more...), then that's almost certainly going to mean one very tired mum.
[My 8 week DS is EBF, and my DP does a night time EBM feed to give me a couple of hours of sleep, and it's a lifesaver for me.]
As SirBoobalot says, we do seem to be desperate to get small babies sleeping through the night. I would LOVE mine too, of course I would - however, the painful truth is that in this instance, what's good for grown ups isn't necessarily good for babies! Dammit.
A small baby needs to feed little but often, not in several big 'meals' - and this means waking often. There is evidence that babies who sleep more lightly, and wake more often are less at risk of SIDS (and the connection between BF-ing and reduced risk of SIDS may be partly due to the way BF babies wake and feed). So, yep, more sleep would be lovely, but my feeling is that it's just not what babies DO, on the whole, and it's not fair or in fact healthy to expect them to have the same sleep patterns as adults. Double dammit.