If you've watched gameplay videos released thus far, deathblows with special animations are all stabs. I guess if you're calculated to do enough damage to kill on a hit, it plays one of those.
Finishing moves is what I thought I saw? I wonder if this relates to "all" swords/daggers? Even in sneak mode>would be straight to a finish move. That is what I assumed.
I think they didn't add spears exactly to avoid the problems of animating different parries against stabs. I would be very surprised if there is a stabbing move in real time (not in a finishing animation).