Skills were introduced later on in BECMI, and they were a part of the Cyclopedia. They called them "non-weapon proficiencies" but they were skills. You are correct that they were based on attribute rolls, however.
But I don't see this working. There is a chasm the players have to jump across. The GM says to BECMI player "Okay roll 1d20 under your Str". Player "Okay, my Str is 17, so here goes my 85% chance of success".
Then he says to player 2, Ms. D&D 3.5 "Okay make a Jump Check, DC 20". Player 2 says "Okay, I have +8 to jump, including my 17 Str, so here goes my 45% chance of success."
Then he says to player 3, D&D 4e Guy "Okay make an Athletics check to make this jump, DC 20". 4e Guy says "No problem, since I'm trained in Athletics, with 17 Str, I have +12 to this check, so that's a 65% chance".
So that's why I'm skeptical of the idea of 3 different styles of play being able to co-exist at the same table. This is what they were saying might be possible; and I'm not saying it isn't. I'm just curious as to how they will do it.