These researchers are forgetting the golden rule that every baby is different.. mine slept alone until 2 months when I had to start work and needed some sleep, at which point he came in with us.
Now at 13 months he sleeps in what I would best describe as a nest (mattress on the floor with a blanket) beside our bed. He went there willingly (the strange child actually comes and fetches me when he thinks it's time for bed, and leads me to the bathroom to brush his teeth!), and has dropped to one feed, and often sleeps all the way through. We're all sleeping better because he'd got big enough that our double bed was rather crowded.
My sister took a different route with the baby always in a cot, and that works for her - both ways are completely valid, both ways work for different people, and both ways have their own risks, hassles, and rewards.
Oh, and mine definitely articulates how happy he is when I join him in his nest for a feed... then just as clearly articulates when it's time for me to get back in my own bed by pushing me away and rolling over!