being a light guy, my experience has pretty much been the opposite. I am certain being light makes it a heck of a lot easier on everything, plus how you ride. I tend to ride "light" by nature anyway.
Makes it easier on equipment sure. With marathon plusses you can always ride lower pressures to make them more comfortable at the expense of speed. However the marathon plus tire is so stiff be default that it really starts to get nice on fast rolling pressures after a certain weight limit passed. Don't really know what the weight limit is, but I certainly pass the limit with gear. Also the noise they make is pretty rad as well.
But to make things a bit easier on both me and my SO i'm using a lighter tire up front (marathon) and a heavier tire in the back (marathon plus). I also have Vittoria Voyager hypers lying around so I might give her one as a front tire, give her a marathon as a rear tire and use a full set of marathon plusses myself. She doesn't break tires nearly as effectively as I do so she might be much better off with lighter tires.