Frustration with calculating outs--the "multiple of 4" rule

[Tical]

So I've been under the impression that after the flop, one can multiply their outs by 4 (subtracting a small amount as the outs get more numerous) and after the turn multiply outs by 2 (adding on a little as the outs grow). This seems like a fairly efficient way to approach the issue, especially at a soft home game.

So why don't any of the poker books acknowledge this idea??? Even HOH (which I'm enjoying because Harrington takes are fairly relaxed and realistic approach to odds/outs)does not discuss this seemingly great way to weigh outs against the pot odds.

Can anybody offer some insight?? Thanks a ton.