Some random points here.
(Disclosure: I'm a professional UI designer with a strong development background. Erstwhile CS dude, but still geek to the core. I consulted with the OP on this article.)
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You really dont know what "16px" means with respect to your OS. The DPI presented to the user is hardware dependent, not OS dependent. True, in certain tablets and phones, the OS and the hardware are bound together (iPads, etc), but not so on the desktop where screens have different DPI (as evidenced by the OP's photos of his screen setup).
This issue is pretty subtle - there's lots of places where ems are the better way to specify point size, like print-centric expereices.
Other experiences, like 10' UI on set top boxes, I could argue that pixels are as good as anything given (a) the huge range of screen sizes and distances-to-screen the interface will find itself in, and (b) pixels are, for all practical purposes, the same as expressing things in percentages (HD being a fixed size), but easier for designers to reason about.
And finally: 12 point on the screen might be some other type size when moving to mobile (probably smaller) and should almost certainly be using different layout techniques when moving to mobile. Line length, inter-line spacing and distance to screen are all in play here, so don't get suckered into the idea that you can spec the text once and expect scaling on the platform to automagically adjust it everywhere.
Related: responsive layout. Spec'ing a type size is really only useful within a known domain range. You should think through the design as you move from platform to platform.
Quite the mess. There's no Grand Unified Theory for this stuff yet. Not sure it even makes sense to go find one. Great design isn't a matter of being uniform, but through being right-for-the-purpose.
That said, the OP is dead on. IF you're in a place where specifying points is the right thing to do, then a point should be a point, not a pixel.
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You really dont know what "16px" means with respect to your OS. The DPI presented to the user is hardware dependent, not OS dependent. True, in certain tablets and phones, the OS and the hardware are bound together (iPads, etc), but not so on the desktop where screens have different DPI (as evidenced by the OP's photos of his screen setup).
This issue is pretty subtle - there's lots of places where ems are the better way to specify point size, like print-centric expereices.
Other experiences, like 10' UI on set top boxes, I could argue that pixels are as good as anything given (a) the huge range of screen sizes and distances-to-screen the interface will find itself in, and (b) pixels are, for all practical purposes, the same as expressing things in percentages (HD being a fixed size), but easier for designers to reason about.
And finally: 12 point on the screen might be some other type size when moving to mobile (probably smaller) and should almost certainly be using different layout techniques when moving to mobile. Line length, inter-line spacing and distance to screen are all in play here, so don't get suckered into the idea that you can spec the text once and expect scaling on the platform to automagically adjust it everywhere.
Related: responsive layout. Spec'ing a type size is really only useful within a known domain range. You should think through the design as you move from platform to platform.
Quite the mess. There's no Grand Unified Theory for this stuff yet. Not sure it even makes sense to go find one. Great design isn't a matter of being uniform, but through being right-for-the-purpose.
That said, the OP is dead on. IF you're in a place where specifying points is the right thing to do, then a point should be a point, not a pixel.