they're doing that it's called reputation, even if you switch sides the faction will acknowledge it, with words like, at least CL know what side to take
Yeah, but I'm talking about conversations in the End Game/After the End wherein people say something reflecting what you've done.
For Instance....
Talking to a NCR Commander, from Forlorn Hope perhaps, after wiping out the CL and he says
"I can't thank you enough son. You helped us secure these lands from those marauding bastards. A few of my men are going out hunting a few CL Remnants down, you want to come along for old times sake?"
or a shop owner saying how happy he is he can trade without fear now.
That kind of thing.
Edit:
Yeah UnDecafIndeed, While I rather like the traditional never ending gameplay I'm quite alright with a concrete ending. I trust Obsidian to actually make several endings for each faction/location/important character, rather than that drivel that Bethesda gave us.