This is the linear curve loaded in the monitor if no calibration software are installed in the system (here you can see the dump). This is the non-so-linear curve which both Spectraview II and Argyll consider linear and load in the video card LUT before doing the calibration (here you can see the dump).
I'm also not sure I understand your question, but regarding your observations, if I'm not mistaken, it's the other way around: Argyll and SVII ramps are linear, and the other values are maybe what you call 'not-so-linear'. The calibration tester 'linear' ramp which is obtained with its reset function ends at 65280, but should imho end at 65535 (hex 0xFFFF) like the other two. Ramp values are (usually) stored as unsigned 16-bit integers with 256 values per channel in an ICC profiles' vcgt tag, with zero as first and 65535 as last value in a linear ramp, so the 257 increment per step is correct in that case.
Regards, Florian Höch