Allow me to say it first. Utter nonsense.
You're missing several things in this analysis. First and most importantly, stats make more difference the higher they get. Take a human fighter with a greatsword for instance. He could have 14 strength without penalties under a weighted system or 16 strength under normal point buy for the cost of an 18 strength under unweighted point buy. Now consider a normal situation: he's facing off against a typical first level foe: an orc in scale mail and a greataxe. The fighter is at +4, +5, or +6 to hit depending upon strength (we're assuming he's got weapon focus). The 14 strength fighter hits 55% of the time. The 16 strength fighter hits 60% of the time, and the 18 strength fighter hits 65% of the time. That may not seem like much but the 10% difference in the 18 and the 14 str fighters' chance to hit is analogous to a 20% miss chance from Blur or Obscuriing Mist.
Now, looking at damage: the 14 strength fighter does a minimum of 5 points of damage. The 16 strength fighter does a minimum of 6 points of damage, and the 18 strength fighter does a minimum of 8 points of damage. If the 14 strength fighter hits the orc, he's only staggered and he can still make an attack. Not so for the 16 strength fighter. With the 18 strength fighter, you can give the orc a barbarian level and max hit points (doubling his CR) and he'll still drop him in a single blow even if he only does average damage. Consequently, the 18 strength fighter is much more likely to single hit kill foes than the weaker fighters and is consequently more likely to survive longer. And because both his attack rating and damage go up with his strength, his average damage per round increases exponentially rather than arithmetically with strength increases.
And all stats are not equal for all classes. A fighter can get by perfectly well with just strength and con. A fighter with an 18 strength, an 18 con, 12 dex, 9 int, 10 wis, and 8 cha. (possible under an unweighted 25 point buy) is simply put a far better fighter than a fighter with 15 strength, 14 con, 13 dex, 12 wis, 10 int, and 10 cha. Similarly, a wizard with an 18 int, 18 con and 13 dex, 10 wis and 8 str, and cha will be a far better wizard than one with the iconic spread. The wizard will know more spells, have DCs 2 points higher (which is like giving the spell focus feat for every school for free), and will have bonus 4th level spells at level 7 and a bonus 5th level spell at level 9 and a bonus 6th level spell at level 12 (unlike the iconic wizard) because of high int.
Not to mention that this wizard will have more than twice as many hit points. And his only disadvantage? He can't carry much without a Heward's Handy Haversack and his melee capability is utterly pathetic (as if that weren't true of all wizards).
There's nothing artificial about it. Specialized characters are just plain more effective in D&D than generalists are. (Bards and Rangers are good generalists and look at how many people complain about how underpowered they are). Just try playing a fighter with a 14 strength next to a fighter with an 18 strength and tell me it doesn't make a difference. The high strength fighter feels like he's doing twice as much damage with every swing. . . .