For 1, porcelain is far more predictable with heat retention than most forms of ceramics. Try pouring a cup of boiling water into a handful of your favorite mugs, and note the temperature difference in a couple minutes. Or pouring less water into some (big difference then). Barring evaporated heat (prevented with a cover), a porcelain will still behave roughly the same with even 1/2 the water it could hold full.

For 2, uh... the better to sip with? * shrug * don't really know.