Slugging Percentage

This guy did his fair share of "slugging".

I don't know why I was wondering this today, but how accurate is slugging percentage? From my understanding, a single counts for 1.000, a double 2.000, a triple 3.000, a home run 4.000, and an out .000. Okay, so why is a triple better than a double in terms of "slugging"? In most instances, a double and triple are hit as hard as the other, but because of speed, someone can get a triple instead of a double. That doesn't seem right. If you're not "slugging" it any farther, than why are you getting 50% more slugging? Also, a home run is not hit twice as far as a double, but it gives the batter twice the slugging percentage. What about the double off the wall versus the home run that just barely clears (or goes off Jose Canseco's head)? It doesn't seem right. What about the bloop double instead of a line-drive single off the wall? Each counts completely different. Does it even out? Even if it does, a triple still shouldn't get more than a double, especially considering many are just doubles with bad defense. Shouldn't slugging perecentage be more of a distance thing, especially because "we have the technology"? Maybe, a ball hit 300 feet or fewer gets 1.000, 301-400 gets 2.000, 401-500 gets 3.000, and 500+ gets 4.000. How does that sound? It seems more accurate to me.