I think that the 70% chance is a good starting baseline, but there are a couple of key issues here before deciding how we can translate this into D&D.
The first is: a 70% chance for who to do what? In computer games, the "who" is probably the average person who is new to the game. The "what", most likely, would be achieving the first explicit or implied objective, which may vary depending on the game: clearing a stage in a shooting game, winning a fight or gaining a level in a RPG, etc. In a D&D, the "who" might similarly be an average person new to the game, and the "what" might be overcoming the first challenge, which, given that it is D&D, is likely to involve some kind of combat.
This means that the 70% chance of success need not hold at the level of individual attack rolls. You could still have a 70% chance of overcoming the challenge overall, even if you chance of hitting your opponent is low, if the opponent had low hit points.
It also means that experienced players might expect a higher success rate than 70%. Just as an experienced player might expect to be almost assured of clearing the first stage of a shooting game, an experienced gamer might expect to be able to use good tactics such as flanking and synergy with other characters to have a better than 70% chance of overcoming his opponents.
The second issue is: ease of retry after failure. In many computer games, retrying after failure is fairly easy - literally, at the touch of a button. In other cases, failure is nonlethal - if you don't succeed the first time, you can keep trying until you do. In standard D&D, failure may result in character death, and a retry is only possible after creating a new character, which may require considerable effort on the part of the player. Because of this, compter games can have a lower standard of success than D&D. The player simply retries until he gets the hang of the game. This suggests that D&D should have at least one of the following: a higher chance of success, a lower chance of character death following failure (possibly increasing the likelihood and length of time that a character will be dying instead of dead), or a quick way to generate a new character so that a player whose character is dead can get back into the game soon.