I think Gruber addresses this pretty well: they already took the silent approach, but it was becoming unsustainable with their pro market, whose needs were not being met. If they just did a small hardware bump, they'd be projecting that they'd given up on the pro and they'd lose a lot of loyalty and goodwill. People can only wait so long so this info helps to keep them interested and bring the term "Apple" back into the vocabulary of any pro considering a future purchase.