Because the outside areas of the scene, and for that matter the mens' jackets are pretty black, with little detail at all, projectors with just "good" black levels look very flat. Below it, is a side by side with the Sony on the left, and Epson 6500UB on the right.
The dynamic iris, with almost all projectors (JVC excepted, as they manage great black levels without a dynamic iris,) of course, is key to the excellent black levels. I figure this is as good a time to comment on the iris's impact on viewing. Below are two images from the beginning of one of the Star Trek movies (The Wrath of Kahn) shot at the exact same exposure! Notice how much brighter the background is on the first image, as the iris is forced to open for the bright credit. (Both images are intentionally overexposed.) A few frames before, without the credit, the scene is just stars, and the iris closes down a good amount. You must concede, the difference is significant. Of course when you have bright areas on an image, you are a little less likely to notice the blacks.