I have played as various playstyles/methods from babarian to alchemist, from mage to necromancer.

But very recently I have noticed on my latest character that I am hearing 'newer' speech from guards and enemies which I've never heard before.

Just now I heard a guard saying "Iron suits you well, it maybe ----- (i forget the rest)" and I also heard a bandit say "Death is greatly exaggerated" just before he dies. I have heard ALOT more newer dialogue but can't remember them off the top of my head.

The script in skyrim is routine and repetitive enough that when something new pops up I take notice.

Any idea if new script/dialogue was added to 9.1 update?

I wouldn't be surprised if the DLC added it.

I think I read somewhere that the 1.9 patch changed the frequency of certain dialogue appearing.

That may be it.

It's nice, because the guards don't bother me about picking locks when I seldom do so.

EDIT: Ah, yes, here we go! From UESP's patch notes:

"Adjusted dialogue priority to improve chances of hearing more combat dialogue from certain NPC enemies"