If you read the tcl2k presentation, you'll see the kinds of things that have to happen to a system as they increase in traffic.
Compare the naive implementation of the Movies site with the one that they endedup with in 3.0. Very different birds, and for very good reasons. Congratulations to them for finding a salable solution.
Last year, I led the team that runs www.ftd.com, a very high-volume flower retailer. For long periods of time, we sustain traffic levels of more than 1 order per second. Think about all the hits that go into completing an order (~~ 100x more). It is a hugely expensive undertaking to build a system that can handle such traffic.
Solutions go to two extremes: extremely expensive Sun hardware (e.g. Enterprise 4500 servers with 12 CPUs) or lots of extremely cheap hardware and a few big scary boxes to handle the databases. We took the 2nd route, and it has worked well. But it takes 30 web servers and a few peripheral machines for monitoring and backup to handle such a load.
Take a look at what google does: http://slashdot.org/articles/00/05/31/1242237.shtml.
