It should drop significantly, for my own personal experience see this linkhttp://billylavoie.blogspot.com/2009/04/sales-stats-for-week.html
This is how the release of my game went last year...things should still be similar
Now this is not the rule, there are other apps that shoots straight to the top 100 and sell like hot cakes....but the top 100 is only 100 apps....out of over 150,000 apps