Sounds typical: they fail inspection for easy-to-see things (e.g., lights missing or warning lights showing), and miss not-so-easy-to-see things (a small amount of leaking fluid).

One things I've heard people say, and which I would agree with, is that one of the reasons to keep your engine bay clean isn't for it to look pretty, but so that problems (esp. leaking fluid or oil) are more obvious. On older cars with dirty engine bays or undersides, it's a lot harder to see some problems because of all the grime. I have no idea if that was an issue with your car, but I can see it being a problem with a lot of inspected cars.