ARM’s Mali Midgard Architecture Explored

Could somebody familiar with the tech explain the Midgard execution model described on page 6 of the article. I don't understand how each arithmetic pipeline of the Midgard is "essentially it's own cpu". If this is the case, it's perfect no as I get an vast array of independent SIMD units. What is the downside?

First PowerVR, now Mali – great news! I wonder if Qualcomm will ever publish some specs on Adreno, though.