I'm both an IT technologist and a published author and technical editor. I was once given a book manuscript to edit and was surprised that it consisted largely of my own published technical articles on the same subject! When I informed the publisher they were sympathetic but didn't want to "make a big deal out of it". They convinced me, against my better judgement, to let them publish the book anyway and give me the royalties. But it didn't sell, largely because it was just a disjoint collection of already published articles.
The moral is that publishers, both print and web, for the most part, don't care about plagiarism.
