No need to look. There IS asymmetry in the damping. It is controlled by two sets of valves... one each for compression and extension. These do control dampening to varying degrees on the compression and extension strokes. Removing damping on the compression stroke entirely would not work as effectively as having some there. While that particular form of damping wouldn't be as noticeable on very rough roads, it would be noticeable on smooth roads. All wheels have at least some imbalance and are constantly subject to smallish imputs from otherwise smooth roads. The smaller resistance in the compression side is very effective in dealing with these smaller imputs. BTW, I used to routinely diagnose flat spotting on tires as an early shock failure on non gas-charged shocks. After removing the shock you could clearly feel the lack of compression resistance on these failed components even though the extension resistance was more substantial.I'll look and the rest of the article and I'm sure i can find a ref to asymmetry in the damping.
No compression resistance in a shock will cause small oscillations in the wheel assembly and ultimately manifest as irregular tire wear.