http://revach.net/article.php?id=2142

Section: Moadim   Category: Pesach
The Brisker Rov - Staying Awake All Pesach Night
Rav Yitzchok Zev Soloveitchik zt”l, The Brisker Rov, always wondered why people are so particular to stay awake the entire night of Shavuos which is a Minhag, while on Pesach night where there is a Halacha Mifureshes to talk about Sipur Yetzias Mitzrayim the entire night until you fall asleep, people are not as diligent.

In fact in Brisk they were not Makpid to stay awake the entire night of Shavuos.  They reasoned that Shavuos was no different than every other night, as Torah is a year round activity.  Moreover learning Shavuos at night is not more important than learning Shavuos by day, unlike Sipur Yetzias Mitzrayim where the mitzva is the night of the Seder. (Uvdos V’Hanhogos L’Bais Brisk vol. 2 p. 79)