It's one of those things everybody knows
<Grumpy old man>
The thing about things everybody knows, is that everybody is usually wrong, to me it's just another abstraction layer, that needs to be managed, and another layer of complexity to inexplicably wrong.
How I long for the days when it was either the computer, the OS or the Application, and where I started in computing even the OS was a layer of computing too much, just the processor and assembler, sometimes even straight machine code. And don't get me started on Glass Teletypes.
So what does your typical n-tier web app. need to run these days.
</Grumpy old man>