Hello Timothy,
excuse my english, i try to explain the best i can.
The reflecting surface is made with a technique called PVD (Physical Vapor Desposition).
The bare reflector spins inside a machine that evaporates aluminium by electricity, the aluminium vapor then settles as a thin film on the surface of the reflector (or any material you put into that machine), making it shiny.
Now if you extend this process and use a little more aluminium for the vapor, you get the same effect as if you used too much paint on a wall, you get an 'Orange Peel' effect on the surface of the material. Also the time used to dry the surface after the vapor application may result in surface effects like OP. Using an already textured molded plastic reflector might be cheaper/easier to coat than using excessive aluminium/changing the dry time on a cnc drilled reflector.
For visualization, put "PVD" or "Physical Vapor Desposition" into Youtube. Edit: Found a good visual
here
I skimmed through the TM16 thread you talked about,
IMHO:
small light -> aluminium reflector all the way, you want to transfer/disperse the heat away as fast as possible when you have limited bodymass
big light -> plastic reflector, because of weight and cost to produce on a mass scale. Heat is easier to transfer in big lights due to the possibilty of adding heatsinks below the LED, therefore lowering the overall weight of the product. I do not think that aluminium reflectors in big lights are usefull, unless the heatsinking under the LED-Die sucks...
Hope this helps!