Several good points have been made about the meaning of selectivity and acceptance rates. It bears repeating, though, that all of the schools being discussed are excellent so try to understand the data should not be seen as a criticism.
Here is a bit of data on the origins of students at Claremont McKenna and Swarthmore. Counting first-year students in 2010, Claremont McKenna had 127 (46.7%) from California. For comparison’s sake, there were 7 from New York. http://chronicle.com/article/Where-Does-Your-Freshman-Class/129547/#id=112260
Swarthmore had 46 (13.3%) from Pennsylvania. There were 39 from California and 45 from New York. So, Swarthmore had essentially equal numbers from Pennsylvania, New York and California, while Claremont McKenna had almost as many students from California alone. http://chronicle.com/article/Where-Does-Your-Freshman-Class/129547/#id=216287
There are also are some interesting patterns in wait lists. For the class of 2017, Claremont McKenna was one of the rare colleges that offered more spots on the wait list than acceptances. There may be a perfectly benign explanation, but it seems odd that the school would put so many on the wait list and then indicate that it was not going to the wait list (yield management?). See http://thechoice.blogs.nytimes.com/2013/05/30/college-admits-2013/?_r=0