I was really curious and it sure looks you are all in the ballpark. I grabbed some web data, made a few assumptions (which could be off for sure), and did some rough calculations.
Annual Attendance at parks (4) and waterparks (2) for 2012 : 17,536,000 + 11,063,000 + 9,998,000 + 9,912,000 + 2,100,000 + 1,929,000 = 52,538,000 // To get per day attendance divide by 365 and you have 143,940Ok We don’t have Disneyquest, some people go to more than one park in a day, and some people onsite take days off to relax or do non-Disney things, but maybe a rough idea of people at a Disney theme park.
There are 30,405 onsite rooms per the unofficial guide. Let’s just go with a US average occupancy rate of 70% and assume onsite guests average one park a day. I'll also make an assumption of three guests per room (lots of families, but couples and solo guests too) // Estimate for onsite guests at a theme park = 68,851 (30,404 * .7 * 3)
So maybe about 44% of the guests are onsite (68,851/143,940) Wow! That’s a lot. As an offsite guest typically I would have never guessed it. But they definitely do have a lot of resorts.