Those kind of charts do make it a bit daft and if you follow cinema guidelines of viewing angle you end up with some very close distances. For example calculated that my 2m wide projector screen at 3m viewing distance is pretty much ideal, but would be silly for day to day viewing.
I think when looking at all the various figures I came up with between 3 and 5 times the width of the screen away was the range to be in. Obviously closer to 3 if you want a bigger experience, and to get more from HD.