Here is
the post where it points out that, not in OD&D, but straight from the basic set, playing a role was the stated intent of the game. When a game states, in the very first lines of its introduction, what type of game it is, for what reason, and what is expected, I find it somewhat disingenuous to explain that, since there are many other things in the book, it is not about that stated intent.
That being said, it is also a game that is played amongst friends, where you don't need to read the book to play, that you are often introduced to by friends who are already playing in a certain style. And god knows that there are many, many ways to play the game. Moreover, after the first CRPGs came out, and a number of these were based on D&D without much roleplay in them, I can also understand a certain drift towards particular forms of playing the game.
My circumstances might have been peculiar, as I had heard about the game in a French magazine about science, but it was impossible to procure it in France, but I mentioned it to the family who hosted me in 1978 (I was 14 at the time), and because they were absolutely brilliant, they found the box for me. It was unfortunately a bit complex, and I was not confident enough to be the DM for a crowd of US teenagers despite their benevolence, so I had to wait for september to be back in France to be the DM for a group of friends from high school.
This means that, for my friends and I, the words in the books, and in particular that introduction, were really the one source that we had about playing the game, apart from that very first article in Science & Vie which very much lacked detail. But, right from the start, our characters had personas, although they were admittedly very basic and copied on characters from Heroic Fantasy that we liked (we had a Gandalf and an Arioch in the very first group, and they did not really see eye to eye in terms of decisions, let me tell you

).
So, in any case, for us, it was obviously the one thing that made the game what it was, compared to a boardgame in particular, roleplaying, acting in character, etc.
Now, from the above, you might think that it was an isolated phenomenon, but we met a few other groups, and soon the french magazine, Casus Belli, came out, and it was obvious from the start that other people were playing the way we were, as a roleplaying game, not an adventure/boardgame, with stories and roles.
I also played with clubs, and although I did not spend a lot of time there, I played with a few people from the famous Rue d'Ulm club, and in particular the French munchkin archetype, Gros Bill. One of the main person in that group was FMF, who actually was invited by EGG to develop games for him in Lake Geneva, and who in particular wrote the AD&D 1e Oriental Adventures.
And one thing I can say is that, although they were huge powergamers (lots of us were at that time), there was a large amount of roleplaying in the games. Actually, FMF has started a while back a
very successful comics in France which recounts some of the adventures of the group, if you can/want to procure it, it's really not bad.
All this to say that there definitely was a congruence about the way we played the game in our groups, the way it was played in France and then back to the US. And I have discussed this with other people who played at the time - some of whom I still play with, by the way - and they have the same views.
Moreover, over my career, I've been an expatriate for years in many countries, and played there. And in particular in the UK, whether it was in a club or with the friends that I met discussing a game of Bushido (and who remain friends to this day), people were playing exactly the same way, with roleplaying always at the forefront of the game.
Has it changed ? Of course it has, I am obviously not the same person that I was when I was 14 and just discovering the book through reading. But not only were the seeds there, but they clearly germinated in many people, most of the hundreds of people that I have gamed with over these many years.
I must also point out that this is not the only game that we played during these first years. We were also huge fans of Runequest, and here is the very first paragraph of a game which, although its contents are even more technical than D&D if you look at them (armor and hit locations, detailed rounds, etc.) is also extremely role focussed in a setting that blows any D&D setting out of the water.
So it was definitely there, although as these games are so rich, they support so many ways of playing them and, as the developers always pointed out, there is no wrong way of playing them as long as you are having fun (and the Runequest guys are the ones who developed the concept of Maximum Game Fun anyway).