Thinking we're getting fractions of pennies instead of our fractions of quarters.

that is my guess as well and one of the main reasons I do not mine on Slush anymore - I get my alt coin payouts steadily on via BTC though - and yes it is pretty much equal to pennies but at least they pay out what they claim they will payout.
Slush has not for a year. If they do now, good - and about damn time.