WebGL dynamic terrain rendering demo

You are correct - it's not depth-of-field, it's fake "tilt-shift" effect that blurs screen non-uniformly based on vertical position of pixels, independently of content.

And I chose it exactly because it's much cheaper than real depth-of-field while looking "good enough" for some type of scenes (it's the same trick many photographers use to get "miniature" feel, instead of using real tilt-shit lenses they apply such blur in Photoshop).