It's made in a less labor intensive way. On Kurosaki's roll forged knives, the spine is of uniform thickness down the full length of the blade until you get to the grind near the tip. The geometry on these knives comes pretty much entirely from how they were ground; they start with a piece of machine-rolled metal of uniform thickness and grind the sides down to add the primary bevel.
Kurosaki's hammer forged blades are thicker near the handle and then thin out as you move toward the tip. This is a product of how the knife was hammered. The sides of the blade near the spine are not of uniform thickness either, and for the same reason. Hammer forged knives begin as a piece of bar stock of uniform thickness, which is heated and smashed under a power hammer and drawn out to the approximate shape of the final blade. The final shape is then cut (or stamped) out and then ground down to add the primary bevel. The geometry of these blades is a product of both forging and the grind.
Which one is "better"? I think neither is better; they're just different.
