That's funny because I don't remember paying for any of the 16 500 mile e-upgrades I received from UA last year, which allowed me to upgrade for free on several UA flights last year. Not a complimentary upgrade in the same sense as NW or CO, but still complimentary.

Along the same lines, AA gives four "free" 500-mile e-upgrade certificates for every 10,000 miles I fly.

I beg to differ. I did actually get one last year. Well, it did help that there were extraordinary circumstances involved. End of the story is that the flight was left three hours late (a 737) with only 9 passengers onboard. I guess I was the only "elite" on board as they only offered a complimentary upgrade to me. One of the other families on board tried to sit up there as well and were sent back to coach. I ended up with my own flight attendant and was offered all 8 breakfasts if I so chose :D But alas, I just took mine and went on my way. Still, the elite status helped, even if it is a low end elite status at that.

The OP didn't write anything about expecting an upgrade. He made a perfectly reasonable inquiry into whether flyers can get upgrades simply by asking. The answer to that, btw, is a qualified yes.

Dress nice, smile, have your paperwork ready, and ask in a polite tone with no hint of demand and it will, upon occasion, work, even on international flights. Delta upgraded me EWR-ATH two years ago. UA did as well to LON. KL to AMS. On a Virgin flight three years back I was actually upgraded after take-off when a FA told me the GA had asked her to move me if possible. (She asked me to be discreet, which I was, and it was fine.) HP routinely upgrades a friend of mine who travels SFO-PHX.

I'm not a good looking, or particularly charming, guy, so others I suspect others would fare even better.

Agreement
 

I have UG on Emirates three times without status by asking in the last 18 mths. I got UG on my birthday on KL and twice last year from very discounted economy to businesses on BA to NY. Each time I was dressed well, empathised with the staff, and asked.

BTW - I did get the latest model Volvo upgraded by asking - its also called 'negotiating'. :-)

UA does offer complimentary upgrades for Elite (GS, 1K, PE, P) who are traveling on certain Y tickets. Problem is that the upgrade is only processed on day of departure if space is available.

I had an op-up flying NRT-SFO on NW a few weeks ago. (and I dont even have NWA status). Just got lucky I guess.

FYI, the fare I got upgraded on was a "K" fare or one of the lowest NW fare classes.