I brought home a bottle and noticed the fill level was way down from where it normally is, with probably an ounce of wine missing. Do wineries do that on purpose? Was I ripped off?
You were ripped off, but probably not in the way you might have considered.
It's unlikely the winery intentionally failed to fill the bottle properly. And by properly I mean within roughly a centimetre of the cork's bottom (assuming the wine was sealed with cork). An air gap of more than roughly two centimetres will cause the wine to oxidize prematurely, and no producer wants wine to go stale before it hits shelves.
I see two strong possibilities. Perhaps there was a bottling-line issue not caught in time. More likely, though, your bottle was the victim of excessive heat exposure. For example: in an unrefrigerated container on a ship crossing the equator or on a long-haul truck on a sunny day. It might even have been stored next to a radiator in the retail store's back room.
Here's a pretty conclusive forensic test. Rub your fingers on the outside of the neck, on the glass just below the plastic or foil capsule. Is there sticky wine residue there? That would suggest the fluid inside expanded enough (due to overheating) to seep out through the gap between the cork and the inside of the neck. It happens more often than you might imagine, especially in summer.
Here's hoping your glass is always full, and your next bottle not half-empty.
The Flavour Principle, by Lucy Waverman and Beppi Crosariol, was named best Canadian Food & Drinks Book in the 2014 Gourmand World Cookbook Awards. Published by HarperCollins.