Update: And from the people who say ratings are both currency AND public speech, there's this reason:
Finally, there was what might be called the Lincoln exception. Nielsen executives pointed to the fact that some schools in a few states – Connecticut, New York, Massachusetts — still close for Lincoln’s actual birthday and perhaps families (some with Nielsen boxes) take vacations then. This would be in addition to what is expected to be some natural falloff in ratings next week when the official Presidents’ Day holiday is celebrated by the nation at large.
That a horde of viewers may have abandoned television this week in honor of Abe seemed unlikely, but, if true, it could cause elevated concern about some other coming dates: Andrew Jackson’s birthday is looming on March 15, James Madison on March 16 and Grover Cleveland on March 18.