Why don't certain sites link?

The thing that REALLY irritates me is when certain sites just copy/paste articles from my blog and then post them to their site without ever referencing my blog.

Whenever I post an article I always try and reference the source I got it from as well as the eventual destination.

I've been changing certain words so I can track who is doing this and I know who you are... it's also fairly obvious when I post an article that was released days before or even weeks before and then it appears on line shortly after I post it.

So those certain sites you know who you are.... show some respect to the Blogosphere and my site by also linking to my blog rather than claiming you've found all this great information!