Re-reading the blog post I see that now.I analyze the numbers both ways--if you just look at OSR systems based directly on B/X or 0D&D, then B/X has more. If you expand the scope to also include OSR systems based on other OSR systems derived from B/X or 0D&D, then 0D&D has a lot more--mostly thanks to The Black Hack and Swords & Wizardry.
Yes, I think first-mover advantage may be significant. I plan to talk about it when I lay out my qualitative analysis in Part 2.
I actually meant products instead of systems, though.
So Drivethru currently lists 915 0e Swords & Wizardry PDFs in its catalogue
While it pegs 1144 for B/X Labyrinth Lord before you get to the new B/X hotness of the 236 B/X Old-School Essentials PDF products.
The drivethru system tags are not as comprehensive as they used to be, I think. I vaguely remember being able to search on black hack before.