...
1. (best method) yourhashrate / 2^32 / difficulty * bitcoinreward
2. yourhashrate / networkhashrate * network blocks per second * bitcoinreward
...
Eh what?
The network hash rate affects your expected earnings? How? Details please ...
Difficulty obviously does, but the network?
He doesn't say that, I think, because (the average of) 1 / networkhashrate * network blocks per second
should be constant for a certain difficulty.
1 and 2 above should be (approximately) equal.