Adult Editions - why not in US?

[Sarah Leigh ...]

 Tonks:
I think it is because adults in the UK are more prim and proper. And in 
the U.S. no one cares what other people think of them. Also maybe there 
is more public transportation in the U.K. where people would be reading 
the books in public. In the U.S. except in big cities, most people have 
cars and read at home. Just my guess.
Tonks_op

Excuse me?!?!
Prim and proper?  
A different cover doesn't disguise the fact that it still says 'Harry 
Potter and the ...' by J K Rowling.  It's just a marketing ploy, that 
we fall for every time because we're afraid of missing something.  No 
one reading a HP book would/should be ashamed of the fact, whether 
American or British.
I am laughing at the prim and proper bit - no one has ever described me 
as that before!!!
Sarah xx