Technical nit: Bluray content is compressed also. What's important is the degree of the compression--which your info did allude to later down-- but wanted to make sure the distinction was clear.
Something else I'd argue is important though, even if _currently_ using a 720p TV, etc, is that at some point in the not too distant future, you might want to upgrade your TV, or might get a faster net connection that supports better quality streaming. On that angle, it might be worth considering a device today that already supports the 1080p.
Great points, for sure, especially the future-proofing. If the rumors are true, and I hope they are, will become a non-issue in about a month...
But based on today's offerings, Roku does have a 1080p model, where the AppleTV is currently 720p.
Regarding bandwidth, I have 18 Megs down, and Netflix HD content starts in under 30 seconds. The iTunes - I have only done items I have previously downloaded to my iMac, and all my devices (iMac, AppleTV, iPhone, AirPort Extreme Base Station) support the fastest available WiFi speeds (802.11n) - So there is no real delay there, either.
As far as "DVR like" that another poster had a question about, yes and no. It is all "on-demand" so to speak (Streaming on Netflix, buying/renting from iTunes), but it is not necessarily as convenient. For instance, Netflix streaming doesn't have new movie releases (some TV content they do, and get updates pretty frequently - Phineas & Ferb and Wizards of Waverley Place come to mind) streaming. iTunes tends to get movies on the same day as the DVD goes on sale, but not all movies are available to rent (HD prices for new release purchases is about $20 a movie to buy, $5 to rent) TV shows on iTunes tend to be available the next day (or some time after 1 AM eastern), so you won't be able to catch tonight's episode of a show until tomorrow, as opposed to starting it when you are ready, but the same night, as a DVR allows. You can also, in iTunes on many shows, buy a Season Pass. What this does is automatically download the next show as it becomes available. I did this with The Walking Dead last year (aired on Sunday nights). I would wake up about 6 AM Monday morning, launch iTunes, and the prior night's episode would start downloading.
A BIG (IMHO) benefit of buying an episode/movie in iTunes, and the AppleTV, is that the content you buy for your AppleTV is also playable on your iPhone, iPod touch, iPad and computer with iTunes, where content on competing boxes is not necessarily (Some might be accomplished via apps)
What I tell people who ask should they go AppleTV or Roku? Do you have an iDevice already (iPhone/iPad/iPod touch)? If so, AppleTV makes the most sense. If not? Which ever you feel will likely be a good choice.
On the topic of "cutting the cable" - I have not gotten there completely. I have reduced my DirecTV package to one they don't advertise, and generally only offer if you are considering canceling, but between the Verizon NFL Mobile App (for Verizon iPhone only), MLB.tv subscription/app, and the Watch ESPN iPhone app, I move closer to being able to. But the content providers are getting "wise" to this - Both the CNN and Watch ESPN apps require you to be an active customer with a participating cable/satellite provider in order to watch live content.