Seth Godin had an interesting post over the weekend: #1 at the Box Office
It turns out that in the last forty years, the length of stay of a typical bestseller at #1 is down by more than 85%. In other words, bestsellers used to be bestsellers for seven times as long as they are now.
This looks suspiciously like the trend noted in my previous post A Game a Day Keeps the Developer's Profits Away in the casual/indie games industry. Hits are hits for only the fraction of the time they used to be.
If your marketing strategy requires you to hit #1 in order to succeed, you probably need a new marketing strategy.