You're right.  I see that.  However, the current round has been running for 16.5 hours.  I brought one of my workers back online about 11 hours ago.  And, the Mhash/s reported for that worker is somewhere around 85% of what my worker is reporting.  And, in the past, this same worker has shown a hash rate on the pool of the same as it's reporting.

I won't be able to tell for sure until the block finishes and the next round starts, but imperial evidence suggests that the reported is _not_ a 60-minute average.  I'll keep an eye on it, but.