On an "advance purchase" / "non-refundable" hotel reservation? You really make those and then are able to cancel them without penalty?

It's not all hotel reservations that charge a fee for cancelling well ahead of time, just the ones that are "advance purchase" / "non-refundable".

But more and more hotels (compared to even a year ago) now charge a fee if you cancel less than a day before the scheduled arrival, on a normal rate. Many hotels that used to allow you to cancel up to 4 pm or so the day of scheduled arrival now require you to cancel 1 day or longer before scheduled arrival, or else you may have to pay the first night's rate. (That's because hotels got tired of too many people cancelling at the last minute, when it was hard to re-fill the rooms.)

It seems to me that you simply haven't been paying attention to cancellation policies and simply got lucky that you never ran into anything like this before.