[HarryT]

Originally Posted by kennyc

But isn't the "point of sale" the user's computer? (even if the price is free )

Certainly it is. But if you, in the United States, choose to download a book from MR that is not in the US public domain, then it's you that's breaking US copyright law, not MR. That's why we have a banner on all the book download pages saying:

This work is in the Canadian public domain OR the copyright holder has given specific permission for distribution. It may still be under copyright in some countries. If you live outside Canada, check your country's copyright laws. If the book is under copyright in your country, do not download or redistribute this work.

ie, it's your responsibility to check before downloading.