|Ghostface Killah - surprisingly not on the Duets album|
It's sampling not stealing. Artists include bits of other songs in their music to create an interesting effect. Van does something similar live and calls them medleys. Sampling is seen by older music fans like myself as evidence that most of the good music was done years. Young fans of the genre see it as another form of creative expression.
Sample-based music has been around for decades. Apparently, copyright regulators are getting tougher with this music phenomenon. Basically, artists have to negotiate a separate sample clearance fee with two different rights-holders: whoever owns the sound recording (the actual sound that's been fixed to magnetic tape, CD, etc.) and the song publisher (who owns rights to the underlying melody and lyrics). For well-known songs, licensing fees can be very expensive and sometimes rights-holders won't agree to a sample clearance for any price.
But it gets way more complicated when you start sampling songs that contain samples, which is increasingly the case today. If you wanted to sample, say, Fight the Power by Public Enemy well, that song contains 20 samples. You'd have to get permission from Def Jam, which owns the sound recording rights, and then Public Enemy's song publisher. Then you'd have to go to the other 20 song publishers and get permission to use their portion of the song.
That's why the more creative sampled music today just isn't cleared at all, in the hopes that rights holders won't sue. But that means that the "legal" sampled songs just aren't nearly as creative. There were some really creative albums early on, back before right holders started demanding huge fees to use a a sample, but those days are long gone.
Here are some samples of Van's music by other artists:
T.B. Sheets (1967) - sampled in Greedy Bitches by Ghostface Killah feat. Redman and Shawn Wigs (2006)
Moondance (1970) - sampled in August's Rhapsody in C Major by Mark Mancina, Freddie Highmore and Jamia Simone Nash (2007) and Ritsy Boss by Lil B (2011)
Brown Eyed Girl (1967) - sampled in Girls, Girls, Girls by Richard Cheese (2004)
Madame George (1968) - sampled in Say Hello, Wave Goodbye by David Gray (1998)
Redwood Tree (1972) - sampled in Struggle by Curse (2006)
Did Ye Get Healed? (1987) - sampled in Featherfunk by Pogo (2012) and Gitch by Pogo (2008)