Pretty much that's how it is. The Majority Leader sets the schedule for the Senate floor, meaning no bill the Majority Leader doesn't want to bring will get floor time for debate and voting. Majority Leaders can do this on behalf of their party, or simply because they do not wish to consider it.
For instance, it was well known that Harry Reid was permanently opposed to patent reform, despite the fact that members of his own party were the ones drafting that legislation
But last May, Leahy announced that he was shelving his patent reform bill, and insiders told me he did this at Reid's request. Reid has a close relationships with trial lawyers' groups, who opposed the bill. Plaintiffs' lawyers were concerned that the bill's "loser pays" provision — which allows winning defendants in patent cases to collect legal fees from plaintiffs — could later be expanded to apply to non-patent cases.
To your second part
Does this mean that even on an issue that has 74-26 support from the minority party and moderates, the leader can always preempt (or indefinitely postpone) voting, and there is nothing that 74 supporting senators can do?
There is something they could do: they could vote in a new Majority Leader with the minority. Of course, that means a split with the party itself, and possibly an election of a member of the minority when your party holds the majority. As such, this type of action is pretty much unheard of, especially in modern times, where party loyalty is paramount.