I am not convinced that Amazon is losing much if any money on Kindle fires. They have far less overhead and far fewer middle men than standard tablets which when coupled with extremely high volume sales and crap hardware can drive there prices vary low.
Amazon has confirmed that they're selling the Kindles at cost hoping to make it up on content. Third parties have done calculations on the Kindles and found the parts and assembly to be higher than the selling price (without taking into consideration things like shipping, warehouses, credit card fees, etc.). Amazon is being above board in saying that they're hoping to make their money back via content.
In terms of the P/E thing, I only brought it up because of how some investors justify Amazon's price. Some investors believe that Amazon will be able to get large market power in certain industries (maybe retail, maybe e-content) and then charge higher prices to get fat margins at the expense of consumers. I don't think that's in Jeff Bezos' ethos (to his credit). However, cornering a market is a strategy that companies have done.
We may never find out because Amazon never reveals how many Kindles it sold or whether it really is making money from Kindle, and the whole "financial industry" is complicit in this crime in cheating the naive investor.
For comparison http://www.amazon.com/Coby-Kyros-7-Inch-Android-Multi-Touchs... low end 7" tablet List Price: $179.99, sale price 100$.
PS: Also, Amazon has little control over there P/E, it's investors that are convinced there going to profitably rule retail in a few years.