Dropping (or rather, heavily quantizing) the high frequency components does create runs of zeroes with high probability. The order the components are stored (a

Dropping (or rather, heavily quantizing) the high frequency components does create runs of zeroes with high probability. The order the components are stored (a diagonal zig-zag) pushes the likely-to-be-zero elements together. At higher quality settings you might not have actual runs of zeroes, but you'll at the least have runs of low-entropy values.