Possibly, it was added because Elvis' version is in a different time signature than Bill Monroe's original, and they sound completely different.
Monroe's version was in 3/4 (waltz) time, and Elvis' version was changed to a 4/4 time version.
Had Elvis launched straight into it without this little intro, it may have been too "severe" for some listeners.
Just a thought.
It is also the official state bluegrass song of Kentucky. And Elvis' version is definitely not bluegrass; it's more of a pop tune.