BUT...they made it seem like it would be compatible, and it's not. It was in the speeches and presentations they did...so NO...I don't have a link to their presentations.
They never said it would be compatible even once. Trust me, I've listened to everything they've ever said. They said they'd try to make it as easy to convert as possible, but never said you'd just be able to use old stuff. A couple of times they said that the mechanics would be close enough that you could likely run older adventures with minimal conversion. They said you'd be able to play 2e STYLE characters at a table with 3.5e STYLE characters. Which is possible. One person can just roll stats and choose a race and class, ignore backgrounds entirely and never pick feats or use proficiencies. Another person can create a custom background, take feats to customize their character, and multiclass.
For me, it doesn't feel like the old D&D, any of them. It's a mash of different ideas they had...which has created a totally new game of what they considered core ideas...but combining all of that idea doesn't make a game that feels like the old games...more like a game that feels like none of them. AS I said, most of those I've talked to in my own circles don't seem to have great favoritism towards DDN as far as switching. Many may give it a try when it's released, but the only ones that seem somewhat more on board would be the 3e players not playing PF, and some of the 4e players that have not been put off by WotC.
To me, the core of 2e (my first version of D&D) was:
-fast play with a minimal amount of mechanics getting in the way of the game
-most of the game being in description with periodic stat checks to accomplish things
-fast character creation that didn't require much expertise. Just pick a race and class and write down what abilities they give you.
Which is pretty much the feeling I get from D&D Next. The mechanics are far from identical, but compare this to my experience with both 3e/3.5e/4e where focus on the mechanics was pretty much the entire point of the game and it feels MUCH more like 2e than any of those editions.
A rough example of play:
2e:
"I search the door for traps."
"Alright, make your find traps roll."
"I make it."
"Alright, you find a trap."
"I disable it. I make my roll."
"Alright, you disable it. On the other side are some Orcs. Roll for initiative."
"You go first, what do you do?"
"I move over and attack the Orc on the left. I hit AC -2 for 10 points of damage."
"He dies. Next person goes."
3e/3.5e:
"I search the door for traps."
"Are you a Rogue? Do you have the ability to find magic traps?"
"Yes. I make a 35 because of the magic item I have on as well as this feat that adds +5, as well as my PrC feature that adds another +5, does that make it?"
"Yes, that would make every trap DC in this entire dungeon. And the ones I will design for characters 10 levels above you."
"I disable it with a 40 because of a bunch more feats and class features."
"Alright, you disable it. On the other side of the door are a bunch of Orcs."
"Orcs? What are they wearing? Do they look higher than first level?"
"One of them has full plate on and a tower shield. One of them is in robes and has a staff with a glowing gem in it and is wearing a necklace. The rest all have Hide Armor and axes. Roll for initiative."
"Wait. Shouldn't we get a surprise round since they were unaware of our presence when we opened the door?"
"No, you weren't aware of their presence either. The rules state that if neither side is aware of each other's presence then there is no surprise round. Roll for initiative."
"Alright, I go first. I move over to the one in the back and attack."
"Then these two get Attacks of Opportunity."
"No they don't, they haven't acted yet."
"Oh, right. This one can, however, since he has the feat that allows him to. He attacks and hits for 10 damage."
"Wait, I didn't know he could do that. I tumble through his threatened squares then. I succeed."
"Fine, he doesn't hit you."
"I attack, using power attack for 5 points. Also, I activate my feat that means if I hit, I will knock him down. I hit AC 35 and do 55 points of damage."
"He dies...and is knocked down I suppose."
"Since he died, that triggers my other feat and allows me a free move over to the next Orc and I attack him as well. I hit AC 33 and do 45 damage."
"He dies too. Next."
4e:
"I search the door for traps. I get a 25."
"You find the trap."
"I disable. I get a 30."
"You disable. On the other side are a bunch of Orcs."
"I make my knowledge check. I get a 30. I know everything about them."
"This one over here is an Orc Shaman. He has the ability to cast curses and shoot fire. He has resistance to fire. This one over here is an Orc Barbarian. He hits really hard and knocks people down with his attacks. These are Orc Soldiers and wear heavy armor and their defenses go up when they are next to each other. Roll for initiative."
"I activate my daily power that gives me +10 to initiative. I go first. I use 'Speed of the Gods' in order to move 10 squares over to him then make a Close Burst 5 attack that hits these 4 Orcs. I hit only 2 of them. They both take 15 damage and are Dazed and have a -2 to hit until the start of my next turn."
"This Orc takes his Immediate Reaction to getting hit and hits you back. He hits AC 23 for 15 damage."
"I use my encounter power 'Unnecessary Toughness' and reduce the damage by 10."
"Alright, next person."
D&D Next:
"I search the door for traps."
"Alright, make your find traps roll."
"I get 17."
"Alright, you find a trap."
"I disable it. I get 19."
"Alright, you disable it. On the other side are some Orcs. Roll for initiative."
"You go first, what do you do?"
"I move over and attack the Orc on the left. I hit AC 16 for 10 points of damage."
"He dies. Next person goes."
So far, in actual play D&D Next is absolutely the closest to older editions out of anything since 2e.