Rich,
Normally it isn't due to an issue in the update. Most of the time it is that the update specifically focused on one thing and the developers had multiple things addressed in the next. So they remove the update only effecting a single addressed issue to a more thorough update. If that makes sense..
So in sense they create an update (hypothetically) for the iDrac to improve connection speeds, but after creating that update they create one that does the same improvement, as well as addresses a reported issue. They pull the stand alone update to go with the update covering more bases.
Now that doesn't mean that you aren't also correct as well. It is generally a mix of the two.
That being said I would update the servers to the most current versions to be safe anyways.
Let me know if this helps.