That's unfortunate, but my team builds the web apps, not the Office website. And the web apps do officially support the latest versions of Safari and Firefox.
All I can offer about the Office site is that it works perfectly in Opera 10, including the Silverlight video. :p
Office Live is actually something else; I believe it's a cloud storage/sync service for Office 2007. The first link you had was the correct one for Office 2010, which includes the Web Apps. http://office2010themovie.com is another, though I have to say I think it's a bit strange. There's some interesting stuff on there, though unfortunately the web apps video (the Terry Crowley one) doesn't have much in the way of product or technical detail.
Wow, this is kind of a confusing mess of branding and offers.
Agreed...the Office 2010 The Movie thing is a bit weird. In general, while it's improving, I think Microsoft's marketing is pretty poor. That said, you are mixing preview sites for Office 2010 (again, I don't know why there are two - that is bad) and current services for Office 2007.