I think these devices should give the user the choice of what method to use. There may be some people that prefer to start playback right away but with really ugly picture quality for several seconds, and people that may prefer to wait a few seconds to buffer and start playback properly, at full quality.
However, I did some comparisons last night between my Panasonic BD65 and this Roku, and it seems to me that the Roku needs some work in the network circuitry. I used the same exact LAN cable for this, and played the same title, which I was an episode of Caprica. With the Panasonic, when I select play, it shows the test bar on the bottom right corner, which quickly goes up to HD and then it buffers pretty fast and starts playing HD. The Roku, just a minute later after I connected the same LAN cable to it, shows only one progress bar that buffers slower than the Panasonic, but unlike the Panasonic, it starts playing at this horrible picture quality and goes up to HD after several seconds. So it's not even that the Panasonic is taking more time to buffer, in fact it's taking less time, and it starts playback in HD, and this is also after a search, in which the Roku is terrible because like I said in my first post, it goes into a lower quality stream before it starts getting better. And I'm taking about a Panasonic from 2009, I suppose the new ones have to be better, although I don't know for sure.
Regardless, I'm not going to pay $100 for something that only streams and does a rather poor job at it compared to what I already have. In any case, I'll spend those $100 in a new Panasonic Blu-ray player to get DD and subtitles.