Windows Phone 7 has a unique user experience unlike other typical user interfaces that incorporate icons, their navigation is block driven. Since applications can be built in .NET and Silverlight, any Microsoft developer out there can develop for the phone or port their current apps or games easily to the phone. That IS a big deal since there are a crapload of Microsoft developers out there – no doubt you're going to see a huge number of business applications built for the device.
The speaker explains that apps are approved, but through a less stringent process than Apple utilizes. They believe it will be somewhere in between the wild west of Droid and the overly controlling process of Apple. Check out what he says at about 9:25… oops!