You can delete them from your Apps and your computer in the same way as you can delete music, right mouse, delete and say yes to remove from computer and app goes to the recycle bin.
But I've noticed on my phone, in the new page we now have in app store for 'purchased' Apps I have deleted from my computer are in the list as it is a record of all apps bought rather than the apps you have decided to keep, so you will see them again on there. Mind you it's a long list on mine and no rhyme nor reason to the order it appears! There's no search function so far as I can see and it takes a while to scroll down and see everything, particularly when the signal is not strong so the screen is slow to refresh.
