I've had games not record time because I was in offline mode on vacation and I pre-downloaded it, or I just played in offline mode or directly from a game's executable without steam's crap embedded.

In the past it's been trivial to set achievement unlocks and time played with 3rd party tools too.

I don't see any kind of discounts mentioned either. I almost never buy from steam directly, usually reputable 3rd party sites like Fanatical, GamersGate, WinGameStore etc that I find through isthereanydeal. It'll show as being on my account but nobody knows what I paid for it and I almost never pay MSRP.

Then there's the countless bundle keys I used to get that I definitely never played and will never play because I wanted 2-3 games in a bundle of 10-20 that was cheaper than one of the games alone.

It wouldn't shock me at all if there was 10 billion worth of unplayed games though. I have friends that buy all the hot releases and then barely touch them because a couple hundred bucks a month is not significant to their monthly budget.