Ride quality across coilover brands is VASTLY different. Tuning, spring rates, how well they're matched, etc is huge. Not to mention quality of components, etc.
The engineering that goes into Ohlins, KW, etc. is why they cost so much. It's also how they can handle well and still have ride quality. Budget coilovers (BC Racing, etc.) have come a LONG way, but the gap is still pretty big to the top stuff.