For the lay person, can you explain "zero-variance" again in real-dollar terms?

For example, we all know the difficulty now is 1,379,223, which currently yields and approx of .73 BTC / day, 22.17 BTC a month

and is set to go up to 1,571,848 which will yield less.

The question then is, as difficulty goes up, safe to assume that the yield in BTC will decrease right?