I think they were designed to draw IN girls that do not find the other Lego sets interesting in the slightest bit-- like my 9 year old DD.
As for the "breasts" issue, women have breasts. All Barbies have them, Disney brand barbie-like dolls have them, Polly Pockets have them (built into their clothing)... Why can't female Lego dolls have them?
But why do they NEED them? Why does the emphasis need to be there from such a young age? American Girl dolls don't have breasts. Barbie's little sister Kelley dolls don't have breasts. I can think of many other examples of "girl" toys where the manufacturer did not feel the need to hyper-sexualize their products.
Has anyone seen the Star Wars Princess Leia "slave" figure? She is wearing a bra with drawn on cleavage.

Personally, I'd rather my kid have a female Lego figure with an accurate body shape wearing a shirt than a flat figure in a bra.
That is a movie specific, role specific figure. What about the Standard Princess Leia Minifigure? Or the Endor Leia Figure? Or Elizabeth Turner? Or the postwoman?
In the original movie, George Lucas went so far as to tape down Carrie Fsher's breasts because he did not want Princess Leia's sexuality to be the focus of her character.
And as for the "skinny arms", as PP said, it is a LEGO FIGURE!!! All lego figures have skinny arms. Most of them are also the same height. It's not like they have singled out the women to be thinner than the men. Why not also have an issue that they make the male figures too skinny? I mean, there are a lot of overweight boys playing with skinny Lego figures, why is that not an issue for anyone???
Minifigures were always minifigure shaped. The legs were square, so i don't see the reference you are trying to make, sorry.
These new "friend" figures are designed more to a human body shape, and in proportion to the body the arms are very thin.
Also, the friend figures aren't the same height.
Kids play with what they like. If no kids like these new products then they will eventually disappear from the market. If people would stop being paranoid that their are "hidden agendas" on products and turning it into an issue, the world would be a better place. Just see it for what it truly is... A TOY.