I think the judgement is excessive but that they likely plagiarized the song. People who are saying that the younger generation does not listen to the Marvin Gaye song, I doubt listen to much urban radio or attend clubs that play that kind of misic. Mashup/megamixes of the two songs are common for both. Many people are only familiar with Thicke's music due to this song, but he has been a mainstay on radio stations targeted towards black people for over a decade. This song, like many of his others played heavily and the similarity was instantly noticed. You would be hard pressed to find an urban radio station that did not play a version similar to this at some point well nefore the lawsuit:
Robin Thicke feat. Marvin Gaye - Got To Give Up The Blurred Lines (Mashup):
https://youtu.be/dhr3XL78mk8Add to the fact that the producer has used a similar tactic with other hit songs and it becomes more suspicious. Nelly's "Hot In Here" was likely ripped from the go-go song "Bustin' Loose" with Nelly even sneaking in the lyric "I feel like bustin loose".
With that said, the settlement is ridiculous and I hate that family members can sponge off of the work of dead relatives almost perpetually.