Yes.
More then that, 4e hosts itself up as a team based combat game, where each member is meant to contribute as much as they can to the team during the fight. As such, you have a responsibility to your team and to your other players to be good at your job.
If you're in a fight and your leader slacks off, it's not just him that loses fun, but the whole team. 4e has, if anything, made it MORE important to optimize yourself.
It is very hard in 4E to make a character who is useless. You could still end up with a useless
player, admittedly - someone who built an illegal character, doesn't know how to play the game, and doesn't participate in combats. But that's an issue independant of system.
4E, though, makes it so that for even inexperienced players, you can typically have a functional and capable character that contribues well to each encounter. No optimization required.
In the end, an optimized character will always be more capable than a non-optimized character (at whatever they specifically optimize for). This can't be avoided without removing the entire concept of choices in character creation (class, ability scores, feats, etc). However, 4E tries to much more tightly restrict how far a character can expand upward from the average, while also trying to make it difficult for one to accidently create a useless character.
The second they have, I think, succeeded at quite well. The first.... they've definitely make a good attempt, certainly. Making it harder to stack bonuses, and standardizing certain elements like adding 1/2 level to attack, results in a much tighter range of results. As more splatbooks come out, and more power creep arises, an optimized character can get farther and farther ahead - but even then, I don't think it is yet nearly as extreme as it used to get. An average character and an optimized character can typically both take part in the same combat and each feel effective - the optimized character might feel significantly more so, might even be dealing out twice as much damage or so forth, but rarely will their capability be so far ahead that the other character is trivialized, or that the other character is incapable of helping against an enemy that is genuinely challenging to the optimized character.