A Tough Sell
Multiple posts on the plastic being cost related, but the current gen was hampered by cost. Sony users gladly pay the "Apple Tax"

but see it from a new user's perspective.
The PRS350 is still available at Target online (link).
It prices at $179 USD. If you get the same page I did, at the bottom are related readers, including the Amazon Kindle, multiple
larger display models priced at $139. I'm no Kindle user, but even I thought "no brainer, I'm picking the Kindle."
That's why it's a tough sell. Even a die-hard Sony fan, who loves his 350, decided on the Kindle when seeing prices side-by-side. Imagine the reaction new buyers have!
I'm sure that plastic saves a significant amount of money. It's a bummer, but inevitable. Really, I'm surprised if anyone new to e-Readers even considered a Sony after seeing the price difference.
-Pie