A Cell processor cost ~$38 to manufacture in 2009, by now I can't imagine it costing more than $20, and even that is a generous estimate. They could have sold a premium SKU for $100 more and still turned a profit, but they chose not to.
I think you're being a little naive if you think
a) That definitely ensures a profit (we won't know the PS4 parts estimate alone till launch/after launch). The non-BC PS4 may have to ride with a small loss to start with, especially if a new move camera/headset is being included.
b) $100 more on top of whatever the PS4 is will be a reasonable price for a large enough audience to warrant it.
If a PS3 launches at $400, you really think people will be wanting to spend $500?
Then you have to consider how long do they continue to maintain factory lines producing the BC SKU and the non-BC SKU (something which adds to costs as well)? Indefinitely?
This generation has shown a mish-mash of SKUs has been anything but successful (Xbox 360 launching without a hard drive, PS3 being too costly and hugely hurting Sony).
You have to streamline, you have to allow consumers to use their own hard drives and then the rest is history. No confusion, no cost-cutting measures to save your company involving taking features away, and no money grabbing tactics like no hard drive/built in WiFi to annoy developers and consumers.