This question stems from watching Rasmus Lerdorf\'s talk from Drupalcon. This question and his talk have nothing specifically to do with Drupal, by the way... it was just gi
The important thing is that you use a web framework that supports scalability through methods like load-balancing and declarative code.
No, a single-entry point does not in itself make a bottleneck. The front page of Google gets a lot of hits, but they have lots of servers.
So the answer is: It doesn't matter.