Seriously, how would someone who has lived in apartments for their entire life before buying a home know to do this???
I figure it was common sense to either know to do it or to know to ask someone what to do when buying a house. If you buy anything expensive, you look for flaws before buying. It shouldn't matter if it were a house or a car or whatever. I hope you wouldn't buy a used car without a test drive. Same goes with a house. Test it.
There are only a few things that you can test (like the plumbing). So, do them. A good inspector only does what a careful layperson should do. Check out things that you would care about. Does hot air reach the bedroom when you turn on the furnace? What about cold air with the AC? Try both, because you'll want both to work when you have the house. Do the toilets work? Are the walls straight? Is there obvious water damage (discoloration, bubbles, etc)? Are their cracks in the exposed floor joists or the foundation? Is the siding/roofing on tight or is it coming off? Is the carpet attached to the floor or is it just lazilly flopped over a rotten subfloor? Is the floor bowing underneath you as you walk? Is furniture covering a problem spot? Etc.
No inspector can pull off sheetrock and look at real problems. They can only look for surface issues. And you can do that too pretty easilly if you just spend an hour in each room. You should want to do it since you are the one forking over $100k - $1M for your first house.
Even if you think you have a good inspector, you should do it all yourself too. That way, you can be confident with the inspector's report. That way you can catch what the inspector WILL miss (like the plumbing in the OP's case). That way, you know what to do in your final walkthrough for problems that the inspector couldn't see (such as what was underneath furniture).