We'll listen to Toyota first. Their press release claims that at the end of April, 504,700 Prius units had been sold, a feat that took the company just under eight years (the Prius was introduced in late 1997 in Japan and in the U.S. in July 2000). By May of this year, 266, 212 Prius cars had been sold in the U.S. OK, that's all well and good, but if Toyota is announcing the half-million number in June 2006, why does some people's conventional Internet wisdom tell us that late 2005 was when the magic (and arbitrary) 500,000 mark was reached?
Take, for example, this article in Consumer Affairs from last November, which says, "Toyota has sold more than 500,000 of the Prius hybrids, setting the mark in October amid continuing complaints about gasoline mileage claims." Or this from Car Buyer's Notebook, also from late November: "Toyota recently announced they broke the 500,000 unit mark in Prius sales worldwide, with about half of those sold in the U.S."
It seems the reason everyone thinks half a million Priuses were sold half a year ago is that late last year Toyota announced they had sold 500,000 hybrids, and people took that to mean Priuses. Just goes to show how powerful the Prius name is when it comes to Toyota and hybrids. Sorry, Lexus RX400h.
[Source: Toyota Motor Sales, U.S.A., Inc.]