Well, I had a look again yesterday morning. Went on another PC and played the trailer for the same movie. Same old slow download rate. Then I went to Amazon's troubleshooting area and saw that such issues can sometimes be resolved by rebooting the modem/router and so I did that. Immediately I saw 480 and a decent picture. On regular Amazon Instant (streaming, non Prime)I am not sure one gets real HD. Has anyone seen more than 480 on that? At 480 I do not think I would have a complaint for $1.99 a pop.
Interestingly also, I got a mail from Amazon asking me to rate the audio and video playback and I checked "awful", the lowest rating and in the comments stated I doubt I would rent again. Will see what happens.
Assassin HTPC + Echo, Sony 49XBR850, McIntosh MX151, MC202, MC7104, MS300, B+W 803D2, CWM's, Janus 1W Sub