It is used as an additioanl emphisis, saying 'Yes' is simply to agree with the previous speaker, but saying 'Absolutely' is to agree strongly with the point or question given.
It doesn't irritate me, I've never noticed it, although I bet I will now!
Affirmative
Agreed
Amen brother
AOK
Ay aye
Correct
Approved
Double negatory
Fair enough
I concur
Indeed
Kum ba yah
No problemmo
OK okay
Okey doke
Okaly dokaly
Oui
Praise the Lord
Quite
Right on
Roger
Si
Sure as shootin�
Sure thing
That�s a fact Jack
Truly
Uh-huh
Very True
Why not?
Without a doubt
Yah Yea yeah yeowsa yep yepperdoodles
Yesireebob
You aint lyin�
You bet
You know it
Yup
Certainly
Definitely
Exactly
Obviously
Positively
Precisely
Surely
Totally
Unquestionably
Utterly
Verily