* 2012-2013: 38,828 applied, 2210 accepted
* 2011-2012: 36,631 applied, 2427 accepted
* 2010-2011: 34,348 applied, 2427 accepted
* 2009-2010: 32,000 applied, 2300 accepted
There's a constant amount of spots and they take the same amount of people.
The reason they are now more selective (percentage-wise) is simply that more people applied.
A more accurate description would be "Stanford's increased marketing efforts got more people to apply". It's a trend nationwide, a race to the bottom to game the school rankings system.
Edit: It's not limited to undergrad programs either. Business schools are at it as well.
Edit2: It helps their top line too. Application fees are something like $100, marketing costs are definitely an order of magnitude smaller, and the cost of processing one application (especially if they just get rejected right away) is quite minimal.
32,000 applicants * $100 = $3.2M
That's chump change for Stanford. They have an $18B endowment and massive tuition revenue.
The idea that they run their application program as a profit center is ridiculous.
And while some schools may "game the school rankings system," Stanford hardly needs to.
But I think you underestimate the need for Stanford to do everything it takes to get maximize their rankings. Most college applicants base their college choice largely on rankings, and the best students are going to be the most likely to give $$$ "back to the school" (whatever that means). If every other top college (I guess the "Ivy+" schools) is trying their darnedest to inflate their ranking metrics, then Stanford is eventually going to find itself towards the bottom half of the top 10 schools with respect to rankings. That will actually affect its long term student body quality in ways that it doesn't want.
Now I personally don't think rankings mean anything, but this is me, 10+ years after my own college applications. From the school's perspective, they have to protect their ranking.
There are very few economies of a scale in an admissions office. Each additional application takes an extra half hours to read. Thus, a certain number of additional applications will require an additional Admissions Officer to be hired.
(No, they're not that well-paid. Remember that applications are typically read by two admissions officers, that they have to meet to discuss candidates, and that the reading season only lasts from December to March. The other 2/3 of their time is thus spent on "marketing" activities, like going to college fairs. But it's not like you can eliminate this expense to cut the application fees -- the admissions staff has to have something to do during the rest of the year.)
Because costs scale in direct proportion to the number of applications received, application fees are a natural way to pay for it.
a 10% variation isn't what I'd call 'constant' exactly.