The essay linked by the OP says this:
It was copyright law, however, that made the old school renaissance possible. Copyright can be very complicated, especially in the internet age, but one thing remains clear: you cannot copyright game rules. You can copyright their presentation, the associated artwork, and the accompanying text, but not the rules themselves: that a dwarf gets a constitution bonus +1 cannot be copyrighted.
The earliest iterations of OSR games, like the Old School Reference and Index Compilation, are simply various editions of the early D&D rules with new art and accompanying text offered as PDFs (often free) or print-on-demand at cost.
To the best of my knowledge this is just wrong. As I understand it, all the retro-clones use the OGL. Checking my own copies, this is certainly the case for OSRIC, Basic Fantasy, Labyrinth Lord and Lamentations of the Flame Princess. Which is to say that they are made possible not by the law of copyright, but the law of contract: WotC has licensed the use of its IP in return for users agreeing to be bound by the terms of the OGL, which puts more limits on the use of WotC IP than copyright law (and trademark law also) would impose on such use.
For what it's worth, I don't think the discussion of the relationship between 4e and roleplaying is any more accurate (I'll leave 3E players to make their own judgements).
The idea that combat is more prevalent mechanically is also not accurate, in my view - Moldvay Basic, for instance, has action resolution rules for combat, and for running away from combat, and for not much else - looking for secret doors and traps, listening at doors and opening doors. And reading the frequently-touted description of the winning team's play of the original Against the Giants Tournaments (in the Oct 78 number of Dragon), I don't see anything there that would not be at home in more recent editions of D&D.
