I agree with most of what you say but this:
" If you plan to use a dynamic site with a database behind it, then forget about it. They're just not up to the job."
Au contraire, they are quite up to the job. The issue then is less data transfer ( esp with databases that don't always go to persistent storage to retrieve results :-D ) and more CPU power.
The issue is less maintenance ( backup sites can always be brought online and switched over to take the other offline ) or uninterruptable power supplies. The issue is cost vs value.
If the value you want is low volumes ( >1 million complex dynamic page hits per day ) and you aren't doing business critical applications ( such as a banking site or shopping site where a missed transaction equates to money ) then an ATX based board is quite adequate to the task.
Data mirroring can happen without costly RAID by using an ethernet connection and an exit to drive a mirror transaction against a remote version of the database. Maybe one, two hours of programming!
These days a hell of a lot of overkill is ordered by greedy web hosting techies that don't think hard enough about fitness for purpose and try to scare money out of procurement managers ;-)
Frankly I would rather pick up a second hand netfinity for 500 quid but...
I don't know what Wayne uses but it is a good example of a popular site which could easily be hosted on an ATX.
Something like
www.tesco.com should be hosted on special hardware with data and processor redundancy built into the design. But then if you are going to do that use something that has ACID properties to run it on ( like WebSphere, MQSeries and DB2 ).
