Because, unlike the eye, your Samsung isn't a constant display device.
Your eye captures a stream of video information with no frames. It's just a persistent sine wave. There's no "blanking interval" like there is in TVs (I know LCDs don't have a blanking interva, but there's still an equivalent where a pixel isn't being addressed and is sitting idle, slowly dimming), they constantly send a sine wave. Similar to how the difference between an original analog music waveform (our eyes) and the cd sampling rate (digital displays) work. Each rod and cone has it's own nerve signaling path to send down the optic nerve. (it's about 1.2 million nerve fibers.)
Sadly, your TVs pixels are not persistently individually addressed. They have a refresh rate as the system walks through each pixel in the grid. The key is to do the pixel update before it fades so much that we notice it. On larger LCDs, the panels are broken up into multiple panels, so it does multiple panels at once. Our eyes on the other hand, each cone/rod is constantly sending information. Somehow our brain stitches it into our perception of the world around us.
You will also note that the Samsung site says this:
The 2233RZ starts with a 120 Hz signal to create 3D with two fully 60 Hz images.
You're not really seeing 120 Hz. And you have processing circuitry in there to deal with that mucking with it all. If the LCD runs at 60 Hz, and you feed it a 100 Hz signal, that's not an even multiplier of 60, so the panel circuitry has to do some sort of pulldown to sync it with the display. Pull-down circuitry frequently leads to visible judder in images, that's why DVDs mastered at 24 fps don't look right if your TV doesn't have good 3:2 pulldown software. 120Hz is very easily mapped to a 60Hz panel (it just drops every other frame). Since it's a consistent drop-frame effect, your eye smooths it out easily. If it dropped every other frame for 10 frames, then dropped two frames for the next two frames, then back to 1 in 10, etc, your eye would see that. It may even be what's happening.