Same updates are downloading twice

Question

I'm currently in the process of letting my friend use XCode on my Mac to do some development. He's staying at my place this weekend. At first, when he signed into the App Store with his Apple ID, the download of XCode failed. It seemed that this failure was due to my apps trying to update and killing the download somehow.
So, I signed back in to the App store and went to the "Updates" tab to update my apps. After 40 minutes of waiting for iMovie, iPhoto and some other Apps updating, we had the idea that I should just "purchase" XCode, because it is free. As we had switched accounts, I was asked to enter my payment information before downloading XCode. At that point I realized that I had already "purchased" XCode, but never downloaded it.
So, I went to the "Purchased" tab. To my suprise, there were "Update" buttons for all the apps that had just updated. Thinking that these were small updates that were recognized after the previous updates had completed, I clicked the "Update All" button. In a disheartening turn of events, a progress bar appeared again for the 1.15GB download of iMovie. It was clear that the App Store was now downloading all of the apps from scratch, for the second time.
My friend, who is a web developer, says this means the following:
1. The App store application does not send a signal from the "Updates" tab to the "Purchased" tab when an app finishes downloading. This signal would tell the Purchased tab to update its list of apps to be updated.
2. The "Updates" view and the "Purchased" view actually store the URL of the .app to be updated, rather than check for a new version upon clicking the button. This is bad because it is very cheap to check for a new version upon clicking the button, but very expensive to re-download a 1GB+ file from an old URL. This in fact costs Apple bandwidth.
3. The "Update" and "Update All" button handlers do not check if the latest version of the App has in fact already been installed. It just goes ahead and starts downloading the same version of the app again.
4. Whoever wrote the "Update" and "Purhased" tab on the App store development team is a novice who doesn't consider these scenarios that would waste the user's time and waste Apple's bandwidth. The basic rule of the day is that if you have an "Update" button, do not have it sit there with a cached URL. Re-check if the app actually needs to be download upon clicking the button, to save a meaningless 1GB+ download.

Answer 1

A song with an iCloud icon has not been downloaded so cannot be deleted. You can prevent it from showing on the iPhone but you can't delete a song that has not been transferred from your iTunes library or that has not been downloaded from iCloud.
Any chance some of the songs were purchased twice - once in the past from a different album and again recently?
To prevent iCloud songs from appearing on the iPhone, go to Settings > iTunes & App Store and under Show All, turn  Music off.