Can gaming consoles be used as a Bitcoin mining platform? I'm very new to the concept of Bitcoin (having only just read the wikipedia entry and visited bitcoin.org)

My question is this: why is the mining platform limited to PC/ traditional computing devices? It seems that gaming platforms would also work quite well, having better performance specs than the general user would reasonably have on his/her home PC and they have networking capabilities.
When CPU mining was common gaming consoles did provide comparable performance.  There was some development work for xbox360 and PS3.  However roughly a year ago GPU mining hit bitcoin network rendering CPU miners obsolete almost overnight. Using unified shaders in modern GPUs and OpenCL programming language GPU miners could operate in parallel working on many hashes simultaneously.  Even the earliest crudest implementations vastly outperformed any CPU in terms of raw hashing power, hashing power per dollar, and hashing power per watt.  Since then refinement of OpenCL kernels have only widened that performance differential.  Currently there is no economic value in using CPU for mining Bitcoins.  

Due to the emergence of GPU mining there are a couple issues that make mining with current gaming consoles futile.


Marketing aside gaming consoles are not that powerful.  Today a $69 AMD graphic card has more computing power than either the Xbox 360 or PS3.  Moore's law is a powerful force and gaming consoles which were start of the art in 2005 are pitifully weak compared to hardware available today.
As already discussed CPU mining is futile and unprofitable
The GPU in both consoles while powerful at one time are rather lackluster by todays standards.  They could provide low end hashing power except they lack unified shaders which makes programming them to do hashing impossible.


Consoles are not upgradable and that is both a benefit and detriment.  Right now we are at the tail end of ther current consoles lifecycle and it works against using consoles for computing power.  Since they can't be upgraded they are essentially $600 computers based on hardware available in 2005.  However at the begining of a console life cycle the hardware is rather powerful for the price point and they are routinely subsidized. At launch a $400 xbox 360 contained about $500 worth of hardware.

So to answer your question there is no benefit to mining on current gen consoles, however it may be possible that "next-gen" console would be viable hasing platforms at least for the first couple years (before their static hardware fall behind due to the continually effect of Moore's law).

However there are some requirements for a future console to be a viable hashing platform:


The Console has a GPU with unified shaders and good integer
performance.
The ability to access those shader either through API (Microsoft
XNA) or hacking/rooting console.
Powerful GPU relative to retail cost of the machine.  


It remains to be seen if future consoles could be used for hashing but using current generation consoles for hashing is simply not economical.