That's what I thought, but I've just had a look here:
http://www.fifa.com/aboutfifa/footb...upport/refereeing/laws-of-the-game/index.html and I can't find any reference to impeding either. In any case, the 'impeding' law only applies/applied when the ball was out of both players' range, eg both running towards the ball and one deliberately changes direction to stop or slow down the other.
Then you didn't look hard enough. The actual quote from Law 12 on the site you mention is:
An indirect free kick is also awarded to the opposing team if, in the opinion of the referee, a player:
plays in a dangerous manner
impedes the progress of an opponent
prevents the goalkeeper from releasing the ball from his hands
commits any other offence, not previously mentioned in Law 12, for which play is stopped to caution or send off a player
If preventing an opponent from getting at the ball isn't "impeding the progress of an opponent", I don't know what is.
The law doesn't need changing, it just needs refs to enforce it properly.