Steam have decided to released a native (well not really) version of Steam for Linux so users no longer have to run Steam through Wine which is a Windows emulator.
The only problem is the .deb released will only work properly on Ubuntu.
So Valve seems to think all Linux users use Ubuntu.
Why couldn't they make a tar.gz which I could extract and compile, or a shell script?
VirtualBox have a shell script version of their software that runs fine, why couldn't Steam do the same?
There are ways to get it working on Debian but this involves cross-packaging with Ubuntu which is deadly to your package system and can create many problems.
So in short: Valve get your finger out and provide a Steam client for GNU/Linux as you stated!! Not Steam for Ubuntu.
An whilst I'm at it, Ubuntu is shite. You might as well use Windows 8 especially with Gnome's latest interface (hollow points at the idiot(s) at gnome who wanted to change the interface to what it is now). Debian even changed their default display manager to XFCE4 because it was so damn awful.