Consider an end-user accessing two content providers, A and B, of the same type. If the end-user's ISP prioritizes A-traffic over B-traffic, the end-user may experience A-content with significantly better quality, and the ISP is said to apply "traffic differentiation." We observe that edge caching has a similar effect: if the end-user's ISP hosts a cache that serves A-content with higher hit rate than B-content, the end-user may experience A-content with significantly better quality. Hence, we examine caching as differentiation: We consider 5 popular caching providers, measure the hit rates with which they serve different content, and use the measurements to quantify the impact of edge caching on end-user Quality of Experience (QoE). We present the—in our opinion—surprising QoE disparities that result from edge caching and discuss their implications.