@Maestrobjwa - It's important to remember that return periods are averages - they aren't always exact. I agree we do seem to be getting less frequent big snows - but it varies. You could go 2 or 3 years in a row with HECS and then nothing for a decade - just as easily as you could go 6 without one and then just have one. It's not something that fits a mold every time.
If science worked that way, we'd probably be staring down the barrel of a Yellowstone eruption (on geologic timescales at least) - as some science indicates it can go off once every 600K years and hasn't in 640K.