D65 is the sRGB whitepoint mostly because it is the CIE Standard D Series Illuminant, i.e it is a Standard illuminant like A and should be use preferably when typical daylight modeling is required. A display by tuning of the primaries intensity can match a lot of different whitepoint, reaching anything from D50 to D90 is certainly doable.
D50 and D65 are the 1960s replacements for illuminants B and C, which were introduced along with the CIE standard observer in 1931.
Illuminant A is a black body radiator that approximates an incandescent light bulb. Illuminants B and C are attempts to approximate daylight by putting a colored liquid filter in front of the black body radiator (or incandescent bulb). Illuminant B is a simulation of tropical noon daylight, while Illuminant C is a simulation of average daylight at a higher latitude (more contribution from the sky, less from direct sunlight).
Illuminant C was widely used in colorimetry, but it didn't match real measured daylight spectra especially closely, so the D illuminants are a replacement based on some physical measurements taken in Rochester (where Kodak was based) and London. Colorimetric applications that previously used illuminant C mostly switched to D65 instead.
(Note that real outdoor daylight spectra vary dramatically depending on place, time, and weather conditions.)
> reason D65 is chosen for the sRGB white point is that it is fairly accurate, in other words it's pretty close to the actual white point of the monitor I'm looking at now (Dell P2415Q).
There is also influence the other way. Monitors have a D65 white point to match the spec.
