I guess our laws are probably a little different, and I have to admit I haven't studied them a lot.
Laws aside, it does seem plain good manners to mention if you have copied a pattern or were inspired by someone else's work.
Many patterns you buy here have a note by the designer saying you cannot sell the finished product (quilt, bag, whatever) without permission from the designer.
There is a local designer who does amazing work here, and she has in her patterns that you can make and sell 5 without having to ask, as long as she is acknowledged as the designer.