When I fly Qantas to Vancouver I connect with Alaska Airlines. It's the only American plane company I've flown with, and they're actually pretty good other than having really old planes.
On our wedding trip over they were the only airline that gave us a free first class upgrade because we were getting married, despite being the only company we hadn't actually booked with directly (just went through Qantas).
I fly American Airlines predominantly (Executive Platinum on AA since I live at their main hub).
From my experience and observation, this is pretty much how seating in first class works:
1) Full fair paid (people who purchased first class tickets)
2) Airline miles upgrade (same airline members only. see sub list)
-a) Executive Platinum (or other airline equivalent)
-b) Platinum, Gold and so on (or other airline equivalent)
3) Airline miles upgrade (credit card miles, American Express, gifted miles, etc)
4) Airline upgrade points (same hierarchy as before, Exec, Platinum, Gold, etc)
Only after all of this, will they actually start handing out the freebie upgrades.
Usually it goes in the following order (but is usually at the discretion of the gate agent, then the flight attendants):
1) Airline club members (Exec, Platinum, Gold, etc)
2) In uniform military service members
3) Anyone else a gate agent feels like being nice to (like people getting married, grandmother's birthday bash in Cancun, etc)
Not to diminish your wedding or anything but if they didn't have the seats to give out, you wouldn't have had the upgrade obviously.
One thing I have observed on a plane that I always thought was very cool was when someone from First Class would walk back to the econo seats and thank a uniformed military service member for their service by trading seats with them for the flight. Always compelled me to buy the guy a drink for his gratitude (if it was the Friday flight home of course).
And a final word to the wise:
NEVER EVER treat the gate agents with less than a respectful tone.
They are travel Gods as far as you are concerned. At the click of a button they can ground your ass for days on end if they want, or have you hauled off by TSA for looking at them weird.
I once dated a flight attendant who taught me that and showed me an example first hand:
We were waiting on standby for a flight and the terminal was very crowded, board was full of standbys. There was a slim to none chance we were getting on a flight any time within the next 24 hours when a woman walked up and started screaming at the gate agent about not getting tickets on the next flight. The gate agent then sent her to sit down after advising her she wasn't getting on that plane. She immediately called us up to the counter and gave us the seats (one being first class) and advised us "That woman just guaranteed herself a seat in the terminal for the next two days for that little stunt, now you get hers" --- seriously guys, if you want to be an asshole traveler, keep smiling at the gate agents.