Max would be a very different character - and thus, Leftover Soup would be a very different strip - if she had bigass pair of jugs.
I've commented on Max's femininity and self-image and such before, but I think it's worth exploring from the perspective of her being an embodiment of my id and an avatar of extreme immoderation.
I suppose everyone, to some extent, takes pride in their appearance, and customizes their meatshell to reflect certain aspects of their inner selves. Max, though (much like myself) doesn't really have a sartorial setting between Comfy and Off. She is, most often, in a t-shirt and jeans - any more than that is dressing up, and dressing up is work.
And, to Max, this is enough. She literally is female, and therefore doesn't feel the need to be feminine, in much the same way that I've always had confidence in my own maleness, and therefore not really felt pressured to develop biceps and abs. If biceps and abs were to magically sprout into place on me, I'd be ecstatic - in much the same way that Max would be ecstatic with magical D-cups - but I've never really felt un-male without them.
I think, though, that where my male experience differs from Max's female experience is in terms of desirability. In a well-known study, men were approached by a female stranger who point-blank asked them for sex - and the vast majority of them said yes. (When the genders were reversed, of course, women were rather less receptive.) For someone like Max, for whom sexual intercourse is the be-all-end-all and obvious end-goal of attractiveness, she's aware that while giant boobs would be nice, she doesn't need them. Max, with her default appearance, is confident in her ability to attract members of the opposite sex in a way that I, in my default appearance, would simply find impossible.