Manufacturing costs are a big part of it. Its safe to assume the AF Sensors for a given segment (often as much a differentiator as megapixels in DSLRs) are fair

Manufacturing costs are a big part of it. Its safe to assume the AF Sensors for a given segment (often as much a differentiator as megapixels in DSLRs) are fairly custom/proprietary widgets and thus more expensive, compared to Sensors where often costs are more amortized (i.e. Nikon using Sony sensors.)