You know how these things go. Don't invite your sister Kim if you want to be the center of attention at your own birthday party. As with any Kardashian personal event, Khloe's 30th birthday proved to be a TV exploitable event for the entire family, including Kim Kardashian who showed off her mammoth mammaries to ensure every paparazzi camera within ten miles of the Isle of Manhattan was trained on her chest. If you got it, flaunt it, baby. I'm sure Khloe wasn't happy, but then her personal wishes have to be sacrificed for the betterment of the entire gentleman ogling community which got two acres of Kim rack in the exchange.
I've never been a sister, or a girl, except occasionally in my dreams. I'm guessing this kind of upstaging does not go unnoticed. I know I noticed it. I suppose Kim will tell her little sister, hey, I can't help it, this is just how I was drawn. And she may just be right. Enjoy.