If you understood the rules of Bitcoin mining to begin with, you'd know that there are increment periods when the difficulty changes. The higher the difficulty, the less one Gigahash will pay out. This rule applies when more people fire up more mining equipment that procures higher mining rates. It's never a constant. Because of this difficulty rule, you once could mine a whole Bitcoin with just a CPU from a laptop. Now, you need specialized ASIC equipment to accomplish the same thing. This rule also applies if they pull the plug. When the difficulty adjusts and goes down, the BTC per GH will go up.

BCS uses the basis of predictable income, so our payouts will be mostly the same every day (until difficulty changes). This helps ensure that luck isn't in our income factor, so we don't go earning more or less. It's a safety sort of thing. If what BCS mines is lower due to bad luck, BCS makes up the losses. If BCS mines more due to better luck, BCS holds onto that extra to accommodate for the next loss.

Just keep that in mind.