Pre-compiled binaries do exist as ebuilds in portage for some very large apps (i.e. libreoffice, firefox, seamonkey, etc.) however they are not very common (only ~100 ebuilds out of ~17K available on my laptop running unstable aka ~amd64) however there's another option called BINHOST that lets you take prebuild packages on one system and distribute just the binaries to other clients.
There are both public and private binhosts, however Gentoo doesn't officially provide any so you're somehwhat using them at your own risk. It's actually pretty easy to set up your own binhost, and if you are doing anything in scale, it's definitely the way to go (especially if you have standardizes hardware).
The big issue with using binhost, and at least part of the reason why it's not popular (and why you want standard hardware), is because you have to sacrafice optimizations to do so. Unless all the client systems have the same CPU, you have to go with the least common denominator when it comes to optimizations (aka CFLAGS). i.e. if one of your clients is a Core 2 Duo and doesn't support sse3 or newer, you can't build any packages with that CFLAG without risking broken packages on the C2D system. Additionally you have to sacrafice customization with binhosts as all your builds will have the same USE flags.
As both optimization and customization are both features that often attract people to Gentoo, the lack of binhosts and minimal formal binary builds makes a lot of sense.