I feel most of your arguments are weak. The only thing that might prevent Microsoft from penetrating the mainstream market is the price tag. If the XboX One is sold out this Christmas season, I see the One as surpassing the PS4 two years from now simply because it's advertised as a machine that can do more than the PS4. When Best Buy and other stores put up the One and PS4 up for display, the One will have a bigger crowd around the machine simply because people will be dancing and using voice commands to play while the PS4 will have people holding controllers. The Xbox One will practically sell itself to the mainstream market just by displaying what it can do.
Issue here is that people are still going to want to have their tablet/smartphone devices regardless of what overlapping functionality the ONE has. I doubt very much that a large portion of users are going to purchase a ONE just to get similar features from their console. There may be an argument for it if the ONE had the ability to replace your cable box, but it simply doesn't.
This argument is weak because the XboX One is not advertising itself as a replacement for a tablet or smartphone. It's being advertised as a hub to use in conjunction with your smart devices, by the way of Smartglass.
It's nice that the ONE can do all that smart glass pairing stuff and all, but that's more of a "hey that's pretty neat" than functionality that's really a system seller. TBH my personal sentiment, and the sentiment that I hear from a lot of other people is that they don't want to use voice commands or gestures to control their system. It's just as easy (and a lot less embarrassing) to do with a remote or a controller.
This argument is weak because "Pretty Neat" functionality is what sells iphones, ipads, Samsung phones, the Wii, and other devices to the mainstream market. Being unique and innovative sells products. We know this already.
I would argue the casual gamers who were attracted to the Wii and the iPad are not the audience that the Xbox is catering to. Yes they are to a small degree with crappy kinect and other casual games, but they are not making a big play in that arena at the moment. I think the iPad/tablet market has taken a lot of that potential away from the console space anyway. And again the hardcore audience will influence people who pick up a next gen system later down the line.
Pinch to Zoom on phones is the same thing as Grab and Zoom on the One, which is why it seems to me that the mainstream market is exactly what they are targeting. Your argument that the ipad and tablet has taken a lot away from the consoles would also hurt PS4 sales so it really doesn't fit in the PS4 vs XboX one debate. XboX one is trying to position itself as a machine to work along side those devices, creating it's own unique market.
Would be a fair point if most steam users weren't getting most of their games at %50-%90 off. I consider myself pretty hardcore and I still only but 2-3 full price games per year digitally. And you have to also factor in expectations. When people buy a digital game they don't have the expectation (right or wrong) that they should be able to resell the game. The same cannot be said of a physical disk. There is also the issue of being able to use these games in the future. Once the ONE reaches the end of it's lifetime what happens to your games? Do they take the servers hosting all this content offline? Are you still going to be able to access your games in 20-30 years time? With Steam and other PC distribution platforms there is no "next generation." You can continue to access all your content unless Valve somehow goes out of business.
Steam games are cheap because they sell a lot of old games. New releases are always full price. Is there any reason to believe that Microsoft wouldn't sell cross platform old games for the same price as Steam? Green Man sells old cross platform games just as cheap as steam, why wouldn't Microsoft do the same? There's a lot of bad publicity working against Microsoft's DRM right now but it'll pass and people will realize that they really don't care, just like they don't care that Steam games can't be resold.