Also, the LD10 has a significantly larger cone mirror thingie (name?) than the LD15. Perhaps that enables the LD10 to focus the beam into a spotlight more efficiently.

The job of a flashlight designer is tough. They're trying to make flashlights as small as possible, while trying to please customers who value throw more, customers who value flood more, and customers who value both equally. Then, there are people like me who notice the color of the beam and how "natural" it appears. It's a balancing act.