They sell it at a loss in the expectation that they will recover the loss in game sales.
How many games do you think the cluster-makers will purchase?
I love Linux, and I love hacking stuff, but I don't expect a company to lose money so I can hack their stuff.
Besides, I guarantee you that hackers will find a way around this. They always do.
Compare Sony’s PR budget with their loses on people buying PS3s for clusters. I’d bet it’s not even close.
Now, maybe Sony should sell a dedicated LINUX box with clustering support, and sell those at a profit (or charge for the cluster support and/or software). Whole new product line. THAT would be smart!
Perhaps they'd be better off pricing their consoles appropriately.