I disagree. I'd rather have a high quality, watchable image after a couple seconds than a blurry image quickly.
I agree that this would be a desirable setup. However, stopping to rebuffer at a mid-level quality during occasional bandwidth slips (the Roku 1 method) is not preferable to dropping down seamlessly, then going back up as the bandwidth improves (the R2 method).
So I guess the ideal solution (at least to me) is a hybrid of both methods. Buffer to get the highest quality stream possible from the start, then take advantage of adaptive bitrate during playback.
Roku XDS, AppleTV 3rd Gen
15mbps on TWC, DIR-615 Router (wifi-N to Roku)
Panasonic P42ST30 HDTV & BD-85 Blu-ray Player
Onkyo HT-S5400 7.1 system
Netflix, Amazon Prime, Hulu+, season passes, MLB.tv, IW Browser Roksbox