Stippling was copied off the texturing some smiths where doing to metal guns (1911 and BHP's), it was a way to add usable texture to poylmer guns that can be very slick.
Glock eventually responded to what the market (or a percentage of) was doing with their product by introducing the RTF models. I've never held an RTF, but apparently the texture was he11 on clothes for our southern cousins that carry. Glock responded again with the Gen 4 and a new texture, which is a compromise (toned down RTF). I actually like the texture on my G17, if I owned an earlier Gen model I might stipple it...not worth much anyhow.
I still find the RTF Glocks not to do great when covered in oil, sweat or blood --
I'm a stippler, so I do it to all the guns that I can.