Yes, but in the opposite, more relevant way. Slingbox is mainly focused on getting a TV/cable/satellite signal and throwing it to your PC (as well as controlling your box remotely). Yeah, it can be cool -- but it's more of a convenience device rather than something which allows new functionality.
With iTV, the implications are huge. It allows you to throw any signal from anywhere (wirelessly) to your TV. It offers that convenience that Slingbox does, but it also does something else: it gives a strong alternative to cable/satellite services. Large numbers of people have already abandoned traditional content delivery methods for Netflix and the like. iTV has the potential to take the next step -- get rid of the disks.
For me it will rock because I'll use it to play movies backed up on my PC, but the real revolution will come when they hook it up to iTunes (or iShows or whatever). If people can rent or buy movies and shows for prices comparable to Netflix's, it will take off like nobody's business. No driving to the store, no mail, no hooking up your PC to your TV, no fuss. Just use the remote and you're set (inDemand services are already toeing this area, but with highly limited selection and clunky interface).
Show and movie downloads haven't taken off on iTunes because, as cool as computers and iPods are, the experience of a home theater system is unbeatable to many. This device has the potential to introduce digital delivery of video to the mainstream.
Apple will succeed where a lot of companies have failed (and will fail -- no games console will become the multimedia center of the living room) because they are clever, as Google are. Other companies try to put a computer in the living room, but Google and Apple see that content, not devices, are important. It's obnoxious to have a movie on a drive in your bedroom and be asked to transfer it to your office, living room, or otherwise. But when you can access the content remotely, with no rewiring and no moving of hardware... you've got something that will get everyone's attention.