You can install apps from outside of the Google Play store. (and open yourself up to malware)
You open yourself up to malware simply by using the Android platform, as the Google Play store has malware in it. The option is there if you want it. Some people choose to only distribute their apps via their own websites. This is also means people can share the APK files from phones with others. For example, I was running Flipboard on my Galaxy S2 while it was still supposed to be a Galaxy S3 exclusive. You just have to use your common sense like you would on a PC.
Apps can do anything they like in the background. This means that you can have things such as IRC clients for Android, which need to stay connected in the background. (is this something used by a lot of people?)
Probably not, that was just an example. One example of where true multitasking bests Apple's is that apps can only download in the background for ten minutes on iOS. I always sync my Spotify playlists for offline use on my devices. On iOS, I can't just let it sit there because after ten minutes it will stop downloading. I have to keep switching to Spotify every ten minutes so it doesn't stop. On Android it will download everything in the background with no user intervention. This is the same when uploading to Dropbox etc.
You can use live (moving) wallpapers and ones that respond to touch. (i think JB is suppose to address this a bit, but those live wall papers have slowed down the phone in a fairly noticeable way in the past)
It depends on the phone. My HTC Desire, Galaxy S2 and Galaxy S3 have all handled them well.
You can attach any file to and save any file from an e-mail. You can download files in the web browser. You can change the default browser you want to use. (got nothing here. i personally like safari, but i can see the value in chrome)
You can mount your phone as a drive on the PC and copy files to/from it. You can basically use it as a thumb drive. (i don't mean this in a bad way, but if you are nerdy enough to do that then you probably have an account with Dropbox, Skydrive, Google Drive etc. These all become much more viable when you factor in the limited amount of internal storage in the flagship Android phones)
Yeah, but why use the internet when it's not necessary and not needed? File transfers over USB are a lot faster. Why would I want to upload everything to Dropbox rather than simply transfer them onto my phone? I do use Dropbox, but I use it for files that I want to be available everything, and that's not always the case for things I want to store on my phone.
You can change the battery in most Android phones. (again....how many people really do this? I know there are some, but I don't personally know anyone out there that carries a spare battery with them)
Anyone that goes to music festivals or on camping trips probably
I don't use it but the option is there.
You can use MicroSD cards in most Android phones. (lets look at the three "flagship" Android devices right now [One X, Galaxy Nexus, Galaxy SIII], only one of the three have MicroSD slots. seems that the trend for Android OEMs these days is to go away from offering those slots in lieu of cloud storage. meanwhile, i don't know of any android devices that come with 64GB of internal flash storage)
Galaxy S3 will have 64GB storage, but not sure when. During the announcement Samsung said it will come in 16, 32 and 64GB varieties. Cloud storage is good, but there are a number of reasons why internal storage isn't out of the game yet. 1) speed. 2) accessibility. 3) data allowances.