I bought a PPK Interarms stainless to see what the differences were between the Interarms and the S&W. As far as fit and finish, as a machinist and a manufacturer of industrial parts, I don't see any glaringly large differences.
It turns out that the rumors I'd heard about changes to the safety design in the S&W were true, though, and they are substantial. The recall of S&W PPK/S's is because of those changes. I don't know if post recall PPK/S's are being delivered yet or not. I would not buy one until I was
sure it was built post recall, as there are
many stories of people getting their guns back in poor condition, damaged by S&W people who are charged with fixing the bad parts in the safety.
Scratches that weren't there before, all kinds of stories like that, plus a few reports that S&W actually sent new grips because the owner sent cracked grips, or they reset the sights that were off, that sort of thing.
Go to The Walther forum and read about these things in greater detail.
http://www.waltherforums.com/showthread.php?t=10989
Other than the recall problems, some folks complain about the serial number being laser burned down in a slot, where Interarms used the normal method of stamping the ser.#. The Interarms doesn't have the lasered etching of the Walther logo, etc. To me these are not big deals.
The PPK has, as you mentioned, wrap around grips, I personally like the two sided PPK/S grips better, I haven't found nearly as many aftermarket grips for the PPK, and I hate the black plastic originals.
After all the talk about how rotten S&W PPK/S's are, and buying an Interarms PPK, I still like my S&W. Now I guess I'm on some people's "S" list for saying that.
Oh well.