It's a Moving Average.. Looking at the code could be an Exponential Moving Average, which fits in with the whole, black hole, gravity well thing..

http://en.wikipedia.org/wiki/Moving_average

It just changes the blocktime per block, rather than every 2 weeks.

I would be interested in knowing if anyone can think of any Disadvantages to using a moving average as opposed to a fixed 2 week readjust time ?

Or Vice versa..