Of course they're not makign anything yet. But they still need to make the orders for the components long in advance.
I believe you do know what you're talking about with how these orders are made, but I still genuinely think full speed production is NOT happening right now. Maybe by the summer, 3~4 months before release. Not 8 months when the actual design of the PS4 shell might not be finalized.
When Sony starts production in July, It's a little late to call AMD and order CPU's and Samsung to order Memory, they will just reply "sorry but all our production lines or take by MS"
These are orders that go over very large quantities over very long periods. for everyone involved large bulk orders is better, that's why the factories are willing to go lower in price on them, and why Sony wants them because it offers stability and of course lower prices.