Recreating melodies from other songs....

So I heard Linkin Parks Robot Boy yesterday and immediately knew that they "borrowed" the main piano riff from T.I.'s "What You Know" produced by DJ Toomp.

Being that "What You Know" is one of my top hip hop songs of all time I couldn't really get passed it while listening to Linkin Parks song. By no means am I opposed to sampling or recreating a melody or an idea from another song to make something new. I would have to say that Linkin Park is one of my all time favorite bands. It's just that in this instance it was hard to hear their song for what it is and not just hear the melody from T.I.'s song.

Now heres where it gets interesting. I didn't know that DJ Toomp took the idea from Roberta Flacks song "Gone Away" I had assumed that he came up with the idea since it wasn't a sample. The writer for Gone Away "Donnie Hathaway" apparently liked that particular phrasing because he used it in a few songs. See the attached video.

There really is no chord progression that hasn't been played before, but sometimes its just too blatant. Plus most pop/modern music is based around 3 or 4 chords anyway. See the attached video. It's pretty good.

You have to change the tempo, the instrumentation, the time signature,  etc. to come up with something new. There have been a few times where I've been working on what I thought was going to be a great song when I realize that it sounds too much like another song. I didn't knowingly rip off the idea, but once I realized it. I just dropped the song. Why continue?

Anyway, I'm all for recreating a melody and doing something new with it. Just like Dj Toomp did.  I'm also for sampling and recreating something new with it. Just be sure to be creative with what you do. Otherwise at best its just a weak song. At worst its plagiarism. Thoughts?