I'm quite certain it is ventricosa. I got it from a reputable grower at the last Bay Area Carnivorous Plant Society meeting. There is a tag on it indicating that it originally came from Malesiana Tropicals. But you're right as far as the lip (was it peristome?) is red on the other ones. For some reason it is yellow on that one that I posted. As Tony pointed out, this is a young plant. The pitchers become 'waisted' as they mature. I have one that is starting to do that.
To answer your first question, about water in the pitchers, when I first got it, the largest pitcher was probably about 1/3-1/2 full of water. Now I'd say it's gone down to 1/6-1/5 full (+ alot of ants). I'm also concerned about that. I've refrained from adding water though because of other things I've read that suggest that isn't good to do (dilutes digestive capacity). Based on your experience, I might change my mind if I read more suggestions that adding water now would be a good thing to do.
I just saw another thread about lids on the pitchers dying. Mine are starting to do that too. I guess I really should put some priority on getting a mister.
Why is it that it's more important to mist at night? It seems to me that it would be more important to mist in the daytime when the humidity drops (at least in the ambient - on my windowsill). Well, the problem is that I work in the daytime, so I would have to mist in the morning and when I get home in the evening.