Yeah, as DPI for modern displays is getting bigger and bigger, we are gradually entering the DPI hell. Pixels are becoming useless and meaningless measures of whatever. Use angular measures, use linear sizes in inches/cm/mm, adjust display of your content for certain viewing distance. But never more use pixels. When I read someone's blog with centered column width specified in pixels, with huge blank fields on the sides, I am losing the last respects for the web designer who did it. And my screen is only 1280x800 14", 107 DPI. And yeah, font sizes are sometmes given in points, sometimes in pixels.
I think that any size specifications in pixels in HTML CSS should be marked deprecated and eventually forbidden to use. You could not assume any certain pixel size and density any more.