The Dodge Ram Alternator has been "known" about for over a year. The popular rumor was that this would be Ironhide. Then, for whatever reason, the backdoor rumor guys started saying that it was going to be Kup. "Alternators Kup", they'd say (if you missed it the first time). How did this happen? Two words: Head Swap. The Optimus Prime head was never attached to any of the early test versions of the mold. The earliest versions either had an Ironhide head (possibly Skids' head), or a head that resembled Kup's.
If true, it means that someone at Hasbro actually went out of their way to trick the internet fans. To that I say, NICE JOB!

Transfans disclaimer: It's been a MONTH and this is the best you could come up with? That's it, we're calling up P.Prime just as soon as we can save up enough calling card minutes to reach China.
* Possbily just the voices in my head
Update: Another possibility that's been brought to my attention is that Hasbro made this mold Optimus Prime at the request of Takara. Selling a car that nobody in Japan owns as a character that nobody really cares about isn't easy. Though the overall Prime-ish appearance of the legs and arms leads me to believe that this wouldn't be entirely true.
Update: Guess I was wrong (shock!). The above scenario is exactly what happened.