Because honestly, any company with a warchest like Apple's can afford real marketing. Who is this supposed to be targeted at anyway? The readers of Gizmodo and pcmag? Last time I checked, those arent even close to Apple's core market.
These "accidental" losses do not go unnoticed. Every online community, every tech blog, every kid and his dog is talking about the new iPhone. Why spend money when you can do it for free?
I agree with the sentiment that Apple probably wouldn't do this on purpose, but the last lost prototype made it on to the cover of just about every commuter rag in the world... That's a lot of free eyeballs.
Faux Apple mocks and speculation about the new iPhone are on the front of most gadget websites anyway, so I fail to see how they'd gain anything extra from this.