I still fail to comprehend how on Earth could Vista be represented as flat-chested? She's resource-hungry like all fuck, so should have boobs even bigger than XP.
Breasts were originally indicators of the maximum amount of ram but I guess they decided that XP was big enough and to just draw them however they wanted to from there on.
She's probably just loli 'cause she's the new one. Whether or not she ever grows up, of course, is less a question of the metaphor and more of the current value of the DFC.