The maker will have to advise if they void the warranty on such use. But for an Art display I've seen such working and in the repair shops I've see them sitting like that. But only the maker can answer if it voids the warranty.
We're considering an "easel" stand for use with a 60" or larger plasma HDTV, like the Panasonic TC-P65VT50. An example would be (love it or hate it) the Restoration Hardware version.
Has anyone tried this? As large plasmas can be north of 100lbs, I am particularly concerned about whether the HDTV itself is designed to be rested on its bottom edge. (My solution would be to attach a wall mount to the easel.)