I was comparing the Netflix HD streaming on my iMac to the output of my Roku 3, and I discovered that different players get different image and sound quality.
A kind gentleman online pointed me to this chart...
On top of this, if the menu screen on Netflix reads "Available in HD" it will play in HD, but if it reads "Available in HD on your TV" it will only play in HD on specific players. About a third of Netflix's HD content won't play in HD on Apple TV, computers, certain networked blu-ray players and Xbox360. The players that will play these movies in HD include Roku, PS3 and Western Digtal Media Servers. Whether or not a player is able to stream 5:1 sound is a whole different set of players that work and players that don't
Supposedly, it's the same with Hulu+.
When I was shopping for a set top box, they all looked pretty much the same. Now that I understand how it all works, at least for Netflix, some players are much better than others. Worth checking into if you plan to put streaming into your home theater.