I've seen the phantom swipes on my inc but have never tested them. i have an 'original' dinc received the first week after launch. I've seen my inc sitting on my desk at work and swipe screens on its own. zero change in light, no shadows, no touching. this is at work under fluorescent lighting.
my trackpad does feel recessed, and i believe that may be due to a slight gradient which the trackpad has. I can't confirm this as true, it just feels to me that it may dip in ever so slightly. But I am also extremely sensitive to build qualities and the tactile feedback received from inanimate objects.
as for variations in actual trackpad height, this could very well be due mass production variances. for instance, Hart ski's ONE ski from 2009 was on a run of 100. a friend of mine has one of the first 20. he ran into someone with a build number around 80 and the colors were more pastel compared to his, which were much more vibrant. as these skis were produced, the ink Hart was using was most likely applied more heavily in the beginning and less heavy in the end, or something to that nature.
Just as with mass manufacturing, model one dinc may be .0010 millimeters under the surface of the glass and as the machines produced the phones, they slowly and slowly began to produce the trackpad ever so slightly closer to the glass, .0015, .0016, .0017 etc etc.
OR, they are using multiple manufacturing facilities which have slight variances in how their machines calculate certain mathematical algorithms.
Who knows. i think the trackpad is the ugliest part of this devices. it's ribbed, and not for her pleasure, so when you touch it, it creates unwanted friction (to me, atleast), and the silver ring doesn't jive with me. and to top it off, mine feels ever so slightly recessed, which to me is poor build quality. i want it flush and smooth as if not there at all, or blatantly bumped out.