You say Moshe was held to a higher standard. Higher than what? True, Moshe was held to a higher standard than others. However, Moshe wasn't held to a higher standard than Moshe. That is, the standard of conduct expected of Moshe was a standard of conduct befitting of him. That is something of which God is the perfect Judge.
The problem is: We are so far removed from the high level of righteousness achieved by Moshe that we can barely understand what it was that he did wrong. But to say that all people should be judged by the same yardstick is to deny the difference among people.
Furthermore, a leader must consider not only the propriety of an action, but also how others will perceive the action. People look to a Torah leader as an example, and therefore his actions have far reaching effects. The more influential the person, the more careful he has to be in this regard. Since Moshe missed an opportunity as the leader to bring the people to greater heights of spiritual awareness, he lost the privilege of being the leader.
There's another reason Moshe was denied entrance into the Promised Land. That is to enable dispersion when the people of Israel sin, because Moshe symbolizes eternity, as the Torah he passed on is eternal. If he would have brought the people of Israel into the Promised Land they would never have been exiled from it, and when they sinned they would have been destroyed, God forbid, instead of dispersed among the nations.
