That is typical of the A-cats. They have only have one sail to trim and sheet and so can get away with a cleatless mainsheet. It actually forces them to not fall away in a set and forget attitude which is slow on an A-cat. Especially on downwinds.

Other designs however have a strong need for a mainsheet cleat especially the single handed spinnaker boats.

Personally I lean forward a little against the pull of the rear sheeted mainsheet and that feels alright to me. When doublehanding I'm using higher sheet loads and really in that setup I can't hold the sheet for long periods unless I use both hands or the cleat. I'm not sure about the next statement but could it be that doublehanded sheet loads are significantly higher ? It sure feels that way to me.

Wouter