Microsoft's models have clear distinction between them, but I think Sony's PS3 models are designed purely to reduce financial loss for Sony. You just have to look at how similar the hard drive prices are between 60/80 GB to realise that the 80 GB model is a pure money-maker...
In order to have a simple metric for what they want the consumer to think is the best product, they put in different hard drives, and what many people don't notice is that the 60 GB model is actually superior in terms of hardware (almost perfect PS2 compatibility as opposed to software emulation).
About the 65nm and Halo models, I don't think those should be counted. The former's just a normal evolution which happens in all electronic devices, and the latter is simply a limited edition for whoever wants it. It doesn't confuse anyone.
My Mario Kart Wii friend code: 2707-1866-0957
