Intel has a pattern of releasing variations of microarchitectures with higher core counts after their immediate successors have been announced/launched. Think Sandy Bridge-E after Ivy Bridge, Ivy Bridge-E after Haswell, and now Haswell-E.
They probably do this because it's probably to easier to manage the larger die size and greater complexity as the process has matured and yields have improved.
And a lot of the time, many of these CPUs are almost identical to one another. They will take a single CPU and brand it in 10 different ways depending on how it does during manufacturing testing.
For a given CPU that comes off the production line, the max frequency it can run at will vary from chip to chip. As well, if there are dead cores on that chip they can just disable them and sell the chip at a lower price (though, intel may not do this; nvidia has in the past with graphics chips).
"Extreme Edition" is normally what they've done at the end of a lifecycle. Broadwell's been delayed it appears, due to process difficulties possibly? This may fill the gap... a little.
They probably do this because it's probably to easier to manage the larger die size and greater complexity as the process has matured and yields have improved.