I don't think the people who dug Stevie Wonder, Steely Dan or EW&F in the 70's were necessarily smarter than todays pop-crowd-it's just that relatively more sophisticated chords, progressions, melodies, arrangements etc. were cool at the time and since those guys had the talent to pull it off, they went platinum. I don't know really...

I know some people have argued that jazz was still a memory to people then which is why even the pop-crowd could accept these things but if you look at the rock'n'roll/R&B from the mid-late 50's, it was very simplistic from a songwriting standpoint; maybe then the simplicity was a rebellion and a breath of fresh air against the sophistication of not just jazz but also Frank Sinatra, Nat King Cole and even Platters and acts like that... Sort of like punk-rock or Hip-Hop would become later...

Maybe more well-written songs will become a fresh thing but if all those guys like the Weeknd and Frank Ocean and that new Usher-song are indeed the sound of the future (I don't know but that's what people say... or maybe it's already over-hard to know today, LOL), it sort of feels that the next thing will be soundscapes and moods which can of course be sophisticated too but it feels more like a return of 90's Trip-Hop/IDM aesthetics than songwriting (tm)...