> I'm not sure why people are having so much trouble with this question, which can easily be restated as "why can't someone build a laptop that has at least as good a display as what Apple calls a 'retina' display while having the same battery life as an rMBP?"

After the first, short paragraph addressing the strict issue with "retina", the longer, second paragraph of the grandparent post directly answered why that would be the case: competing on different feature trade-offs rather than making the same trade-offs and competing on price allows greater profits because it avoids entering a market with direct substitutes, even if doing so in a way constrained by the trade-offs earlier entrants have made results in entering what is effectively a smaller market without direct substitutes instead of a larger market with direct substitutes.