Disagree. Needing to have units present in a city to be able to see all the surrounding tiles is reasonable and adds an extra strategic factor to where players locate thier units.
(For example some may choose to put all units in border cities and leave internal cities undefended but may then have problems with worked tiles).
b.t.w. if city population is set to work a tile and then it is no longer in vision range next turn, it will still be worked.
City vision is buggy, if you work a distant tile that becomes blackened because of a moved unit the worker 'disappears' (you have to click on the city for him to reappear). But like Lord P says, this adds something to the strategy and I think it should stay.