i think that the interpretation of the lotg is what causes the 'confusion' over this issue
looking at at lotg 12/13 - can't be bothered to check 13/14 - there are 15 bullet points (procedures) under 'the referee must adhere to the following procedure when dealing with injured players'
after these 15 bullet points it then says that 'exceptions to this ruling are to be made only when:
a goalkeeper is injured
a goalkeeper and an outfield player have collided and need immediate attention
players from the same team have collided and need immediate attention
a severe injury has occured, e.g. swallowed tongue, concussion, broken leg'
what it doesn't specify is for which bullet points exceptions can be made
'common sense' means that most referees decide that this means that players can be treated on the field of play / don't have to leave the field of play
but the ruling, the way it is written, could equally apply to, say, not allowing for the full amount of time lost through injury to be played at the end of each period ' or stretcher-bearers entering the field of play without a signal from the referee'