snowe:

But: not using the actual mean and standard deviation will not result in an overall mean of 0 and variance 1 as often desired, right?


Yes, but the propsed method might still work “good enough” for the tutorial. 



 snowe:

Does anyone have a paper or book explaining this (I need a reference for my project  )?


I think you should be able to find a proper explaination in Goodfellow et al., Deep Learning 1 and I’m sure Bishop, Pattern Recognition and Machine Learning 2 explains it as well (which is also a general recommendation to take a look at).