As the 1st Edition DMG humorously put it (page 8)
As this book is the exclusive precinct of the DM, you must view any non-DM player possessing it as something less than worthy of honorable death.
Looking back at at AD&D 1e as the classic example, there was really only one book aimed only the players, the Players handbook which didn't even have combat tables!
And sure there was player support in Dragon magazine and in Unearthed Arcana but the spirit of the game was "Its the DM's world. You just play in it."
What I call Transitional School moved from more to the players game but it was still mostly the still in the hands of the DM. AD&D 2e for example had many many player splats (The Completes) but also mostly DM support.
New School epitomized by 3 and 4e is mostly the players game. There are at least as many "player" books as GM ones and even most support is feats and stuff which are almost entirely used by players.
In 4e, magic items are in the Players Handbook and are basically equipment whereas before they were the DM's purview and treated as rewards.Heck there is even a rumor about eliminating the DM entirely in the future.
These choices made sense from a marketing angle (Players outnumber GM's 4-6 to 1 in most groups) and the rules that constrained DM's (when followed anyway) were more than welcomed by players who had ever suffered under a mediocre DM.
However all those rules can be drudgery and can easily suck the fun from a game. I think as many OSR people have learned Old school in the hands of a good DM is amazingly fun and imaginative in ways that more rules heavy games cannot match. Of course as someone who spent a summer with crud DM's can attest, good DM's are in short supply. So what is a DM especially ones whose players have a lot more choices than they did on a lazy summer day in say 1982 to do?
We here at 5 Stone say, lets do both.
By offering support for Pathfinder we embrace the new school (ironically preferred by the oldest of us Grognards) and the OSR (preferred by yours truly) we offer ready to use fun for everyone.