1. I still don't buy your assertion that the minis focus comes from or is tied up in the roles themselves, as opposed to being an overall focus of 4E.
Well, my assertion is more specific than that: it is that the roles have a strong minis-combat component to them. This does tie them into it to a certain extent, but that extent is variable.
It is also entirely possible that the minis focus can be a concern both of 4e in general, and of the roles.
2. Defenders are all about marking. Defenders are the only class that can assert their own mark at will. While marking is new to 4E, it doesn't in and of itself require minis. You can add Combat Challenge, Divine Challenge, and Swordmage Aegis to AD&D Fighters, Paladins, and Fighter/Mages and they will all work seamlessly with or without minis. Defense is the other half of marking because if you are going to encourage things to hit you, you need to be able to survive doing so or you suck at life.
I disagree that "defenders are all about marking." I think that would be saying "strikers are all about sneak attack." The latter is a subset of the former, but it's not a necessary requirement for the former.
In other words, you can have a 4e defender who doesn't mark, in the same way you can have a 4e striker that doesn't have sneak attacks, or a 4e leader that doesn't have healer's lore. There are many ways to accomplish that same goal. Marking is certainly one of them, but marking isn't the goal.
Part of what a 4e Defender is about, though, is limiting the movement of its enemies. Attacks of opportunity, the aegis, the divine challenge -- all have a component of motion to them (the aegis perhaps most expressly).
3. 4E itself is all about moving pieces of plastic. The roles are simply a reflection of this. They are not the source.
I don't think I said they were the source. I did say they had this component. It makes sense that they have this component, since, as you say, 4e is all about it.
5. Defenders have always existed. They have existed in that they attempted to do what 4E Defenders did, and weren't as effective at it because they lacked the marks.
In 4e, Defender means something more specific than "guy with high AC." In earlier editions, the fighter was more specific than "guy with high AC," and filled some different roles in the "first one to 0 looses" combat system, as well as in the dungeon exploration portion of the game.
It's over-simplifying things, and ignoring what other fighters were actually designed to do (which wasn't just "provoke attacks." Though 4e defenders, in part, do this).
6. While the 1E Fighter didn't have the tools the 4E Fighter does, he attempts to achieve the same end.
That's really the core of our disagreement. I don't think so. I don't think so at all.
The 4e fighter is a minis combat class. It does things in minis combat. It revolves around minis combat. It focuses on minis combat. It does virtually nothing not related to minis combat (some skills, I guess?). It revolves around each individual combat (encounter powers, for instance). It exists in order to facilitate minis combat. In 4e, your fighter is supposed to stop you from being hurt by your enemies in minis combat.
The 1e fighter is a dungeon exploration class. It does things for dungeon exploration (mostly, fighting). It focuses on dungeon exploration. The reason it exists is for dungeon exploration. In 1e, your fighter is supposed to be the first one into the dungeon and the last one out. That's it's function -- to survive and be consistent.
Rather than seeing the 1e fighter as poorly designed, I see it as designed for a totally different goal. It wasn't designed to give a balanced combat option. It was designed to give you an interesting dungeon exploration option.