First, I have no insider information. I don't know anyone that works at Apple. So my conclusions are based on 'public' observations only. They're just guesses.
That said... I would guess that the next version of Front Row will support live/DVR TV. At least analog, if not digital (aka HD.) Why? Because of one little line on Apple's Leopard Preview
Accessibility page:
Now, why would they need to support closed captioning in analog broadcasts? The Mac doesn't presently support 'analog broadcasts' without first converting them to nice digital files. That leads me to think that the OS (or QuickTime, anyway,) will natively support TV tuners. Apple doesn't tend to add things like that unless they plan on using it themselves. (Inkwell notwithstanding.) So my guess is that all of the 'consumer' Macs will come with integrated TV tuners at a minimum. Support for third-party TV tuners and/or an Apple-branded external tuner might be included, but I wouldn't count on it.