I really don't see the big deal with Hulu. It is nice that the content is available at one site, but you can get most everything at the individual network's sites already (and over the air). What Hulu really needs to do is cut deals with the cables channels like Syfy, TBS, A&E, TNT & FX. Channels like Discovery will probably want too much money to show up on Hulu (or the Roku) any time soon. Sure, Netflix has some Discovery content, but not much. I would be very happy if Roku could bargain a deal for these channels. I wonder how much they would cost per channel?
To me it's pretty straight forward. If someone is interested in getting access to the current season of shows - as well as past seasons that have yet to make it to Netflix - from ABC, FOX and CBS as well as documentaries and movies (granted the catalog is smaller than) this service fills that niche. As an example, I got the invite to preview Hulu Plus three days ago and I am currently watching full seasons of FlashForward and Modern Family; something not possible with Netflix. Though it's early, I would give Hulu Plus an 8.5/10. I think the $10/month is very reasonable; the video quality via my PS3 is on par with any service (Netflix, Amazon, iTunes, etc.) that I have seen on any platform (Roku, AppleTV, Samsung BD player, Samsung TV, Wii, PS3 and PopcornHour, excluding Vudu on my Samsung BD player; and the UI is easily the best of all the platforms/services noted above.
In my mind, bringing Hulu Plus to the Roku DVP would be a great move. As opposed to it being a case of Netflix vs. Hulu - as I have seen people try to pit the two against each other around the web - I really see them as complementary services. Hulu gives you more immediate access to new content while Netflix meets the needs of those willing to wait for a while to view content. Between them, $19/month is not a lot IMO.
If it does make it to the Roku DVP (fingers crossed) just like all the other channels, users will have a choice. For those that feel $10/month is too much to pay, they simply choose not to add the channel. For those who see it as a niche filler and helping to round out the Roku lineup, they add it.