"this" and "getself" are two names for exactly the same function returning the calling reference.
I'm not sure about this... I recall a thread recently, where it was mentioned that "GetSelf" returns the base Reference on NPCS (hence why Spells get Added to all future versions, for example), and "This" returns the actual instance... But I've not messed with it too much, and can't recall the thread, so I may just be misunderstanding it... The CS Wiki doesn't say anything about this, and does confirm what you're saying that they're the same, so... :shrug:
Edit:
Found it
Well, for the most part, an ability spell will "stay" on ONLY the person you add it to, since it's not on the base object *if* you don't use GetSelf anywhere, since GetSelf can return the base ref on respawnable characters, I'd sift through the entire code and do a replace of "GetSelf" with "This".
From this Thread : http://www.gamesas.com/index.php?/topic/1080073-unholy-darkness-complete-vampire-overhaul/page__hl__GetSelf__st__60
Looking at it, yes, it sounds like I just misinterpeted the meaning (I.e., "GetSelf == BaseRef", This==InstanceRef").