Differentiation’s role in marketing strategy is rethought in this journal article (which builds on an earlier report for corporate members). It presents a small mountain of varied empirical evidence, including direct measures of perceived difference:
(Download journal version of differentiation)
Differentiation (a benefit or “reason to buy” for the consumer) and Distinctiveness (a brand looking like itself) are different things. This isn’t just semantics, as any lawyer or judge will tell you. Distinctiveness (branding) is legally defensible, while differentiation is not (other than time limited patent protection).