What's the different between Gregg Gillis (Girltalk) and Jason Derulo?

I’ve been hearing the song “Whatcha Say” by Jason Derulo quite a lot (listen here). Initially I was going to ask the question “Do you think Jason Derulo received permission from Imogen Heap to use a snippet of her song ‘Hide and Seek’, in his song?”
I realized this isn’t exactly what I mean to ask – as I quite like the artist Girltalk and his ideology about how intellectual property rights should work.
So rather, what’s the difference? Off the cuff, I see that Girltalk’s songs are entirely made up clips of other songs, whereas Jason Derulo mixed Imogen Heap’s clip in which his own track. But I think the crux of the issue might be deeper than that.