I am a grad student married to law enforcement (so one average income, but we have to pay for daycare...ouch!).
Anyhow, I have been saving basically since DH was 1 (before that we saved for medical bills and our trip to CA-
Disneyland, but I am from there). I knew that this year, DS would turn 3 (I wanted to go before I had to pay for him

); I also knew that I would be finishing school this May. (Guess I was ahead of the Celebration theme!) The in-laws are also going, but they are only paying their half. But we are staying in one room (4 adults plus a 2 year old).
We live on a very tight budget that I make every month ahead of time. So anytime we got extra money, I saved some (a few years of some tax return money...if I picked up some part time job money, a year-end bonus one year at DH's work [about $200, gotta love working for the govt], etc.). We also saved any money that DS got for b-days or holidays. I have a separate account with his name on it that earns "good" interest for this reason. I let relatives spoil him at Christmas/b-day and we would only get him a toy or two and put money in the account. Luckily, he isn't old enough to care about gifts. I hope to train him that we do family vacations instead of a bunch of junky toys. DH and I haven't bought each other a gift in years. It is funny, even DS knows that if he gets a card in the mail with money...he has to hand it over to mommy to take to the bank. (He also has a Mickey Mouse piggy bank)
Then, after saving for 2 years or so, with my ILs going, and seeing my tax return, and the 4/3 deal....we are able to stay 6 nights (couldn't find the 7th night! agh!

) at AKL with the basic dining plan. We also don't have to factor in flying as we can drive pretty easily (live in GA). I made a budget with tips, photo pass cd, souvenirs, gasoline, etc. For the 5 of us, for 6 nights, Deluxe resort, wtih dining plan...I had to budget $4700...so our share is $2350.
Now before all the deals, and before I was sure that the in-laws were going. I looked at a room for DH, me, and DS (again 2 so free) at Pop for 4 nights, with dining and park tickets for $1435 or something like that. Even with gas, tips, souvenirs...we could have kept our trip under $1800 and our tax return this year alone was more than that.
I think that you will find that most people who go all the time stay value (or offsite or are more careful about cooking/bringing their own food), have DVC, have 2 incomes (or one really good one), or don't mind credit card debt (like most Americans). It is also a matter of priorities. It probably would have been more responsible of me to save for my retirement or DS college!