They need to, it's where the market is shifting to.Looks like Microsoft is getting serious about these tablet doodads.
People are finding that they don't need a large machine to web browse or enjoy music and video any more.
I think iPads still need to be connected to a computer of sorts for the initial setup, but things like firmware updates and media library management are now features of iOS, forgoing the need of a PC or Mac to perform these tasks.
Plus, Microsoft seems to be putting itself out there with the Smart Glass feature for the Xbox 360. While they said it works with any tablet, I'm sure they'd much rather have people use their hardware.