Obviously to encourage impulse buying. I can't count the number of times I've picked a small set of songs in my shopping cart and ultimately ended up removing some before purchasing.
Check your preferences. iTunes updates seem to reset some settings for me, like the "Keep my iTunes folder organized" setting stuff I have hidden like the TV shows section or Podcasts because I don't use them, etc.
Removal of the shopping cart must have also been because of people like me. I used my shopping cart as sort of a wish list that I would save to and pick from.. reason why is because it was always synced no mater which computer I was on. I had an issue with this a while back where songs had been deleted from the apple store but were in my shopping cart which caused my iTunes to fail... boo that the shopping cart is gone