Thank you Jérôme, great questions!
1. The Float property is needed in Google’s webmail clients, where the CSS table code doesn’t take effect. I touch on this very briefly in the “Calculations for Google’s webmail trio” section:
2. Great catch! This is actually another thing that the display: table; property helps us with. Even though the Google webmail clients don’t make use of the CSS table code for placing columns beside each other, we still get the float-clearing benefit of display: table; here since that part is inlined.