You should be able to find the new video channels right after you update the app. They're only going to be available on iOS and Android versions of Pulse for the time being, so Windows Phone users will simply have to wait. The new channels have their ow section in the catalog and you can add them in exactly the same way as you'd add a new RSS feed.
This is a curious move for Pulse. Oh, I'm not surprised they added videos; I'm interested in the fact that they waited so long. Not that I'm criticizing Pulse, but earlier this year Read It Later changed their name to Pocket. That was a sign that these apps (Pulse, Pocket, Flipboard) were now being used for much more than just reading. The fact that Read It Later's most saved links were usually videos, not articles, gave that detail away months before the name change.
On a related note, I do so wish I could see Pulse's user stats. An increase in video watching suggests a corresponding increase in bandwidth and that users are assuming that it will be there when they need it. That tells me either 3G is cheaper and more common than I expected or that free Wifi is so ubiquitous that everyone simply assumes it will be there, no matter where they are.
Of course, given that most of the people who have apps like Pulse work in an office and spend the majority of their time there or at home, the user stats might also tell us whether these "mobile" apps are really still being used while mobile. I suspect they're not - or at least home/office use is higher than it used to be.
I've noticed, just from my own personal experience, that I'm using far more "mobile" apps while anchored to my office chair than I use while mobile. Right now I have Twiiter and Gmail open on one of my tablets so they'll ping me when new stuff comes in. Sometimes I'll pick them up to respond.
For me, at least, the term mobile is now something of a misnomer.