Was upgraded at WL my first ever time there and to WDW for 8 days from standard to pool view on the 6th floor, was very nice. They just gave it to us, we checked in around 7am.
Also upgraded at AKL this may from standard to animal view but they said it wasnt really an upgrade because those rooms were temporarily downgraded as there were cranes visible in the background, way background too. There were still giraffes, ostriches, zebras and some kinda cattle aplenty right outside our room all the time, that was about a 8am check in. We always fly red eyes.
The reason they upgrade is pretty guessable at any hotel. 1, and unlikely, they have no other room available for the stay you booked because of poor room management meaning you'd have to move mid trip, and they now have to upgrade you.
2) They have rooms available in the higher price category a plenty and not so in the category you're in, they want to make the lower one and the higher one available to possible last minute guests, as being out of the low room rate could mean a loss of sale, and if they have high lvl rooms available too that means keeping both available. The added bonus here is the customer that gets the upgrade is really happy too and is more likely to come back and the hotel really didnt lose money as you can never ever count on an upgrade.
Both of these are just flat our business reasons. We've been really really lucky with room upgrades at deluxes in the two we got, never asked and the second wasn't even a real upgrade. I feel very lucky though. I don't think asking will help you at all because I bet room upgrades are determined by management ahead of time in order to maximize sales, or maybe a really sophisticated program. Who gets them would just be total luck and i bet its just who's vacation fits what is needed the best in terms of length of stay, then its probably first come first serve, but who knows when they update that, could be any time of the day so first come first serve could be 7am one day and 5pm the next.