It's not as simple as you make out, Bleve. In some types of buildings your argument might hold but there are arguments on both sides.
In the absence of smoke, the most effective position for EL is at high level and the most conspicuous position for signs is also at high level.
In the presence of smoke, obviously, the effectiveness of the high level EL and signs will diminish greatly but to be in this position, haven't we missed something. Shouldn't we be aiming to get the people out of the building well before smoke gets into the escape routes in this way?
I will agree, absolutely, that in open plan areas such as nightclubs, assembly venues, trains, coaches and planes, signs and EL should be positioned so that they will still perform their required functions in the presence of smoke but this does not convert to a general rule that all signage and EL should be at a lower level.
Stu