Web font sizes

Text always look small on pages when browsing at a higher resolution on my laptop I notice. Which shows that the web browser is rendering at the dpi level, rather than millimetreage. So 12pt font at 72dpi (28dots per cm) screen res will be 4mm high. If the res is 144dpi that 12pt character will only be 2mm high, which is tiny!

So shouldn't text be rendered at a millimetre size to make it consistent across displays?