Agreed. It would be interesting to see to see a stat on accepted OOS #s vs matriculated.
It seems the OOS applicant pools are so large because it can be filled with people who don't qualify for their IS, they are covering their bases, they are applying b/c its a better fit and their IS is ridiculously high also, maybe a SO lives in that state, or whatever the reason. Many students apply to multiple schools, so while there may be 1000s students trying to get into 20 spots, not all actually want to go there. Not all are even qualified. What's the number of applicants (across the country) versus spots? To me that gives you a better feel for how competitive overall the field itself might be. It's not perfect, but perhaps its a data point that should be considered.
If 10 students each apply to 10 schools looking to occupy 1 of 10 spots (1/school), that seems like you've now got 100 applications for 10 spots. The individual school now publishes their OOS acceptance rate is 10% (1/10). But really in this poor example, all kids get in. No, of course it's not like this for real, I made up numbers to make it easy to show that overall acceptance rates can be a smoke and mirror act depending on how you spin the data.