I don't know who is going to sell more globally, it is bias to think one will outsell the other easily with out evidence
Microsoft came off a complete failure in the original xbox, the xbox 1.5 one year head start didn't do anything didn't create any "mindshare" either. they also ran into the RROD issue which was a billion dollar loss as well as bad PR. the Xbox 360 sales didn't really turn up until the slim revision same with the ps3. controversy sells
This is revisionist history if I ever heard it. Original xbox was a success. Online gaming became the norm. First person shooters became popular on consoles again. Oblivion and Skyrim came from Morrowind on Xbox. Bioware gained console prominence due to KOTOR and Jade Empire. Nvidia bent MS over a barrel on their video chip pricing which is why they were forced to kill the console early. It never made money because of the rush job it was, but it was a fantastic system that introduced 720p gaming and dolby digital sound to the PS2 generation.
Xbox 360 had RROD issues, but it also gained an incredible following due to how complete of a package their online ecosystem was, packaging a headset with every console and having games with full online multiplayer capability right out of the box while Sony was just figuring out how to do it. They also provided an easier to develop platform that allowed their system to simply have better ports of third party titles.
BUT, I do think they're relying on what they did early in this generation too much. Now PSN is a beast and is free. Now XBLA isn't the only game in town for indie devs and Sony has at the very least caught up here. PS+ offers greater value for your dollar than XBL gold now. Kinect was a great counter to the Wii-mote and they will provide that "grandmother approved" gaming experience to replace the Wii, but they're overloading the XBO with the Kinect priority. Now Sony doesn't have the system that is too difficult to squeeze power from. Instead they have the easiest system to squeeze and its also the beefiest in hardware.
And then add on top of this the anti-consumer focus and you end up with a history in which Microsoft really helped shape current gaming, but is in danger of squandering all of its good will by alienating the people they should be catering to.