I'll skip some points where I'd only repeat myself - we'll have to agree to disagree there - and get to where I can say something new.
I'm glad you mentioned D10 (I assume you mean Storyteller). Lots of people consider the WoD games as some of the games that most greatly encourage roleplaying. Yet, the Storyteller system has social mechanics that are way,
way more detailed than D&D - and it even has some mechanics for those non-social events we mentioned before. I think this is a final proof that the presence of social mechanics at least doesn't impede roleplaying, isn't it?
Maybe it even helps it, to a point, and this leads me to the considerations about D&D editions. I've started with OD&D, switched to 2E, and switched to 3E. In OD&D, we did basically no roleplaying as we think about it today, not for several years at least. I think the concept was completely absent; the intro adventure was a dungeon with apparently random rooms and no plot, after all. Nearing the end of our OD&D period, we were occasionally doing something different from fighting, but we were still just playing ourselves in different bodies. I attribute that to the sheer amount of time we'd been playing (5 years), and to the fact that we occasionally played other games.
Enter 2E. For a while, nothing changes. As the DM, I'd like the players to roleplay more, but I can clearly see that they see it as a pointless chore.
Around this time, we also started Vampire. That's when I noticed the weird thing: players would do decent to good roleplaying in Vampire and not in D&D, no matter what. And this even though our Storyteller hardly ever gave XP for interpreting the character, or used the rules about regaining Willpower by following your align... sorry, nature/demeanor.

Back then, I believed that carrot/stick was the way to go to get your players to do something, but here was the proof that I was wrong.
Why?
Enter Planescape.
This is what actually started moving something. A detailed, roleplaying-centered
setting, not a system. It showed that you can do exceptional roleplaying in D&D too, and it didn't need rewards for that. That's what prompted people to start making characters that weren't a bunch of numbers, and it did it
quickly, too.
My conclusions to this point: you want RP, you must have a good setting. The system can only do so much. It's not D10 that does the magic, it's the WoD. It makes lots of sense - the rules are only your interface with the setting, after all. I wonder if your opinion that 2E is the edition which mostly encourages roleplaying is at least based on this? After all, 2E had all the most original and evocative settings of all D&D.
Enter 3E. Boom. We played a short campaign to learn the rules, and then I said "let's start a new PS campaign", and
everyone came up with detailed characters, interesting background, and played them to the hilt. It was...
sudden. Compared to what we had before, it was greatness squared, and it keeps getting better (and it eventually infects newbies, too). Before 3E, we never dreamt of having entire sessions without combat.
So there's more than setting, too. I've been thinking long and hard about this. Here's my opinion: the presence of social skills in D&D 3E says to players "There Is More Than Fighting" on some deep level. That, and the fact that XP are awarded for overcoming challenges rather than killing monsters, and a lot of other nuances. 3E is not perfect in this aspect, but it is far superior to previous editions.
Concluding, I think that having 3E and a
good setting is the best way to get people to enjoy roleplaying. And no, the metasetting that's implied in the game isn't enough, and a homebrew made by a newbie doesn't qualify either.