That’s what those Travelmate things linked a couple posts above mine are. The first time I saw them I thought “Hey, I could just get a baby medicine spoon and make one of these!” but I never got around to it.
As for sleeping strapped to a cliff…uh… no.
I guess that there are two reasons for the zip-loc bags and plastic containers. First; its an environmentally friendly thing, along the lines of the saying… “Take only pictures, leave only footprints”.
Second, it is a matter of courtesy for climbers that might be below you, further down on the cliff face. As somebody else has commented, many big climbs can several days, so while you are sleeping on a bivy after day 2, there may be people 500’ below you sleeping after day 1. Imagine their surprise in the middle of the night if you took the lazy way out!
It sounds pretty gross, but I guess it comes with the terrritory. Personally, I can’t ever see myself even doing 1-day multi-pitch climbs, so its not an issue. 
And then a bird flying by below thinks to itself, “wow, look at that worm sticking out of that big leaf. Time for lunch.”
Mmmm, oh yeah. Oh yeah, don’t stop, mmm… {wakes up} OH GOD! THERE’S A BIRD CHEWING ON MY DICK! GET IT OFF!