Sure, that can happen. However, if it were really true that paying high wages always results in superstar employees whose productivity offsets the additional wages then that would be the norm.
Going for the slippery slope, aren't you? You have a bell curve - paying more lets you get employees from higher up it.
Now I don't think I, or anybody else, have been implying that paying better is the only thing necessary to improve employee quality and productivity. Hell, there have been complaints here about companies treating employees like crap then wondering why they have no retention.
Ultimately you have several factors. Now, remember that this is all 'law of averages'.
1. An employee that feels he's appreciated is more likely to stay and work harder. Pay that scales with the work is one way to show appreciation.
2. More pay will help retain quality workers.
3. More pay will help attract quality workers
4. At some point 'more pay' will cost more than the improvements it brings to the workforce.
Now, thing is, the above requires that you either let the poor performers languish or just plain let them go. Pure pay and crap treatment otherwise is also detrimental.
I don't think those decisions are best made by government decree.
I agree. Note the example I used - Walmart. The example in this thread, The Gap. Both raised their wages without government direction(though one could say there was government encouragement). I'm not saying to raise the minimum wage. But as companies keep discovering and forgetting, how you treat your workers, even the bottom ones, does ultimately affect your business.
Especially if you have a position that requires a fair bit of training, you might want to pay a bit more than minimum wage because if they're 'good', they'll jump ship the moment something better comes up, and now you're out your training.
I don't think those decisions are best made by government decree.
Neither do I.