Pawn Structure Chess

 I see that this classic has been updated.....what exactly has been updated?

I don't know what format the original was published in, but the new edition is algebraic.  They probably checked all the examples with an engine and replaced the few that didn't hold up; that's conjecture on my part though.  Thanks for reminding me about one more great book in my library that remains embarassingly unread...

I have the Mkay edition and it is in algebraic. I was just wondering if the author added some new material. If so it might be worth a purchase......if not.....no purchase

I think there is some confusion here.  Pawn Structure Chess (new edition) by Andrew Soltis is a 2013 copyright by Batsford Chess and is in symbolic notation.  I do not have a copy of the original, but it was a 1975 copyright.  My copy says "Fully updated version of a chess classic." -- whatever that means.

Pawn Power in Chess by Hans Kmoch is a 1959 copyright published by McKay and is in English notation, including my 1964 printing.  I don't think this is the book in question.

No confusion here that I can see, except for the confusion you're introducing by mentioning Kmoch's book. There is a McKay edition of Soltis' Pawn Structure Chess.

the examples are mostly from recent games i'm guessing quite a lot of the book has been rewritten. i dunno if that makes it worth buying the new one though, he is probably telling you exactly the same things just with different examples.  

The Soltis book has obviously been re-written.  A quick thumb through the book shows several games post-1975 including a game in 2011 between Anand and Carlsen.  How much is "new", I don't know.