That sell PS3 copy scheme won't work I don't think.
The exception being stores that don't know better or something, but to my understanding you don't get "A PC copy free with the PS3 copy"
What you get it a "Steam Copy" (PS3 and PC) or an xBox copy.
Portal 2 installs steam on the PS3 requiring your steam login to run, the Steam code verifies them BOTH. Sell the PS3 and the person that gets it can't play because you used the code.
I imagine this was a sick hilarious marketing ploy they used to eliminate the ability for retailers to make a buck off of used PS3 copies. It was probably a happy convenience it would sound great on paper and stir up hype for that particular version.
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But back on topic, I voted PC but I misunderstood the question as a general thing. You should probably clarify you are asking the Escapist what they think YOU should buy. I imagine 90% of the votes are what people think is superior themselves.