thanks for the link to the midnight rider cover. I like that version and have seen the commercial but just put it on my endless songs to track down (most made for commercial songs never become available outside of the commercial - I have a list of many that I wish I could get).
thanks for the Red Hot Chili Peppers song. Had not heard that one yet, but have that album coming my way soon. That is a slap bass line that is the most famous for this (link).
Here is Marcus Miller, he likes to slap his bass... ("Detroit" by Marcus Miller)
"Dark Neccesities" sounds alot like "Can't Stop" reinstrumentalized.
What you are hearing is a song written using scratch guitar. Most songs are usually piano or guitar strum based. Scratch guitar is primarily used for rhythm not for pitch. When you write a song using scratch guitar, the scratch guitar usually gets lost in the mix (pitch wise) so producers usually add strong piano chords to signal the chord changes and/or key changes. Lots of times they will drop the scratch guitar during the verses and then add it back in for the chorus to give an effect of more energy (see "Celebration" by Kool and The Gang below). Dark Neccesities was written on scracth guitar and has the piano, and so do the two Marvin Gaye songs that you referenced. Similar stuff is running thru those songs.
Scratch guitar songs =
"Good Times" by Chic
"Celebration" by Kook and the Gang (they drop the scratch guitar during the verses but keep the heavy piano chord changes)
"Get Lucky" by Daft Punk
"Can't Stop The Feeling" by Justine Timberlake (I think this is the song of the summer for 2016 - the new "Happy")
How to play scratch guitar (different people call it different things) (link)
Here are a few of the songs that I cannot get out of my head (this week):
"Faster Gun" by Little Big Town
"The Worst Is Yet To Come" by Keb Mo
"Sharp Dressed Man" by MOB (Steven Tyler, Johnny Lang, Mick Fleetwood, John MacVie)
"I Have You" by Steve Martin and Edie Brickell
"Eastwood" by Brad Paisley
"Fly" by Jon Stevens