Hey, I just caught your post while checking in here for information on the DX^2. I will try to answer some of these questions as best I can. I currently have a rooted DX with the latest Gingerbread OS.
1. Google maps is currently taking up 9.78 MB of space on my phone which would lead me to believe that the maps are downloaded on the fly. However, this is extremely fast.
2. Itunes is what it is. The native music player for this phone is fairly straight forward and simple to use. There are plenty of others in the market as well.
3. I believe the video recording on the DX is 720p at 30fps. I have always had fantastic video and with the three microphones in the DX I get crystal clear audio as well. I assume this will be the same for the DX2.
4. "Itunes" for video media is called the Gallery. I think that Motorola did a fine job with this app, others may disagree. There is also the 3D Gallery which is more of a google native app. From what I can tell, pictures and video are organized by date within the app.
5. Rooting your phone and installing a custom Rom is truly what separates Android from the iOS. This is a very difficult question to answer though and I would recommend looking in the "All things root" section and reading a step by step guide. Once you have the basics on what it is and how to properly restore your phone if you mess up, the possibilities are endless. This is how I have Gingerbread OS on my phone before the OTA (over the air) that everyone with a DX will get when motorola is ready to release. By the way, I know you said you wanted to keep it stock, but look in these pages, there are devs that do fantastic work with themes and custom roms. Flashing new and different roms is great, just make a back up of what you like so you can always go back.
6. I believe that you can uncheck the option to share data when you first activate or within the settings menu. Honestly, I have nothing to hide so I don't really care. I consider it the same as Backup Assistant from Verizon.
7. This is not a question of whether or not Google will support, but whether the manufacturer will support further updates for their own phones. Google is responsible for the Android Source code which is released as an open source project to manufacturers and anyone who wants it. Motorola has been one of the fastest to release updates, but each manufacturer puts their own spin on Android. This is where you get Motorola's "motoblur", HTC'S "Sense", and Samsungs "Touchwiz" all using android with their own "skin" on top of it. Product differentiation in a nutshell. The Google Nexus one, and Nexus S run just plain old android and have consistently gotten the fastest updates, we're talking days.
8. Last answer, you can still zoom in on web pages using the pinch-zoom gesture and if you want a page to automatically reformat to fit the screen simply double tap it and its done.
Hope some of this helps.
By the way, I've played with the iphone and the whole operating system is just one big app drawer. Android is all about customization and really making your device personal to you and once you understand how Android can really multitask I think you will begin to see the difference.
And now I'm off the soap box.