It's not that 完全マスター is wrong - it is a very good book for getting the basics of the grammar, and I've used it myself a lot in the past. But in order to keeps things from being overwhelming, it tends to leave out some of the finer points of the expressions.
Anyway, those two examples fall into the distinction I made before.
"When it comes to my father (who loves alcohol/to drink), when he drinks he gets so genki it is as if he's a different person."
This would not, as I understand it, work with のこと. As noted above, のこと is used for something that isn't considered normal or expected. People often change a lot when they drink, so something becoming overly energetic doing something they love (drink) can be considered normal.
"For my younger brother, when it comes to cars, all of a sudden its like he is an expert."
Because of のこと, according to the above reference, this implies that the younger brother usually isn't an expert on anything so his expertise on cars is out of the ordinary.
That being said, on looking at this more carefully, this "out of the ordinary" situation can also be used when のこと is not present. So, it feels like while there are often times when they can be used interchangeably, there are also times when this construction (limited to nouns) can be used to show the distinction I initially wrote about.
Thanks for the reply - it forced me to look more closely at was being said and learned a bit myself!