Sampling of music has been prevelent for at least 15 years probably closer to 20 expecially in rap and pop. People do it all the time. As long as it is short then it's free to use, longer pieces do have to be 'footnoted' so to speak. Believe me if he uses too long of a piece, sting and the romantics will be right there demanding thier cut.
The ability to sample free goes on the premise that there are only so many phrases/words/musical combinations in the language and there are going to be things that sound similar, or an artist just wants to give a shout out to something he likes but doesn't use so much that the work is ENTIRELY dependant of the prior musical piece.
Frankly I love hearing samples when they are done well, it's kinda a blast from the past for those of us who have a long and eclectic history with music. I've got everything from LMFAO to Barry Manilow on my playlists and everything in between, sampling or in the style of types of songs are everywhere and I like them, it's just that much more to add to the collection.
Bruno Mars is great at using prior music or music style to do things with a new and inventive twists. He's not my favorite singer but I've got 3 or 4 songs that he's done on my playlists. Lighters is one of my favorites of his (colaboration with Eminem and another young rapper) and is Runaway and The Lazy Song.
I have never thought of him as copying or unoriginal or simplistic. I just think he's a good singer.
One of my favorite user's of sampled music. Pitbull.