Most monitors have a 60Hz refresh rate. Every frame gets duplicated at locked 30FPS and 60FPS is obviously no problem.

40FPS would cause judder because some frames would be displayed twice and some only once.

A good V-sync solution can solve this. Killzone and InFamous had a variable framerate (35-45 fps) and it works great and have that 60 fps feel without stutter (patched InFamous, regular KZ) or tearing. You just have to do a good solution to sync frames and you are good to go.

They didn't mention visuals, just "something that would really impact the player's experience". If, for example, they had to choose between lots crazy set pieces or a locked 60fps, i'd much rather the former. I'm a player. My experience would benefit more from the set pieces.

Opinions are fun o/

You know very well that is debatable. Uncharted 4 is going to be the biggest game yet and everyone knows Naughty Dog had to make sacrifices and use tricks to get the game to run as well as we got it on the PS3 games. If it cannot run at 60 they need to lock it at sub 60. You know very well that Uncharted has a visual reputation and is known for pushing the limits on consoles. Sony already got sued for KZ's multiplayer running at 900p instead of 1080 like the storyline. They should stick to their word. 

Of course it's not going to be 60fps. 30fps locked is the best we can get with those kinds of visuals.

Hey, I have an idea! Instead of 1080p do 900p! There isn't even that much of a difference and you could use that little extra power to you know, have cool things while performing...

...acceptable. I guess.

Get ready for a compromized experience when you finally get to play XCX.

As long as it doesn't drop bellow the 30fps, that's a win for me already. If they can't aim for the 60 though, they should make it variable like in TLOUR.

because TVs work at 60Hz input (even the 100/120/240/480/600/whatever Hz sets, they all really work at 60Hz), so you need to use 30/60 frames in order to have smooth playback

30fps at 60Hz is displayed like this: frame 1, frame 1, frame 2, frame 2, frame 3, frame 3 - every frame is displayed 2 times and that is smooth

60fps ofcourse is just frame 1,frame 2,frame 3 and so on

40fps is displayed likes this: frame 1, frame 1, frame 2, frame 3, frame 3, frame 4, frame 5 - that some frames are just displayed once, while others are displayed twice creates visible stuttering

in the future hopefully even TVs will have adaptable refresh rates (some new PC monitors have that with adaptive synch/free synch/g synch), which makes it possible to lock your game framerates other than pretty much 30 and 60 (15 is unuseable and 120 makes little sense in 60Hz) and still have smooth playback

no it doesnt. all 3 uncharted games and TLoU were 30FPS and all were amazing experiences. 

a better game at 30FPS is preferable than a worse game at 60FPS.