There are a lot of possibilities. You certainly cannot really compare streaming quality service to service by watching
different movies, etc. It could be that you just happened to be watching LaLa when there was high demand on your own broadband at that time (maybe others streaming other stuff at the time). Maybe the pipe itself was unusually in high demand at that particular point in time (maybe everybody in the neighborhood was asking a lot of the community broadband pool). Etc.
Try watching the problematic scenes at several points during the day. Judder every time? Watch it on a Mac or iPhone and see if it judders there too.
As to playing around with settings, there's probably not much there to make a difference. If you want to think it's an individual, "my setup" issue, I'd do some testing with your wifi vs. ethernet connection. For example a pretty simple test would be to temporarily connect "the other way" (ethernet if using wifi now or vice versa) and stream the same scenes again. Judder in the same spots again?
Especially if you are leaning on wifi (as many do), were there other devices in the home in use known to also consume wifi bandwidth and/or interrupt/disrupt wifi? 5 kids streaming 5 videos in other rooms? Etc.
Odds are high that if it's individual, it's probably more in that direction than something in the menus.
An easy(ier?) test would be to take your
TV to a friend's home and thus change everything about your supporting setup. Then run the stream there and see if the judder is in the same spot.
I definitely would NOT be so quick to conclude that iTunes streaming video is compressed more than Google & Amazon, etc. While that could just happen to be true with any one movie, it's probably NOT the case on any universal level. A real test in that direction would be to rent LaLa from those other sources and watch the same problematic scenes through them too.
But maybe someone will do what you ask and chime in with experience with the BD version and confirm or refute the judder on the disc too. You might want to pin down very specific points in the movie where you see the judder, so that a BD owner can jump to those very same points.
One more thing: grain is not necessarily a compression thing at all. Some might even argue that grain is desired for a more authentic movie look. On the flip side, extreme clarity of image can be put down as the "spanish soap opera" effect. All that is somewhat personal preference and director choices.