Because I can't resist the prospect of getting flamed, here is my analogy.
A guy writes down a number from 1-100 on the back of a postcard. You guess what that number is, and if you choose the correct number, you win. You keep guessing as fast as you can.
Every 30 seconds, the guy tears up the postcard and creates another one with a new number.
Can we agree that your previous guesses have no bearing on your chances of choosing the correct number now? Same when a block changes.
Expanding the analogy to include difficulty makes no difference. You now need to choose a number from 1-500, so it's going to take you longer to find a correct answer. But when the guy tears up the postcard and writes down a new number, your previous guesses does not effect your new guesses.
BTW: I am all for lowering difficulty to reduce *variance*, and I'm sure there is some flaw in that analogy, so flame away
