Ive heard the statement that casuals dont notice the difference in framerates, aspecially on B3D, but frankly, i find it to be a completely retarted statement.
People notice 60fps over 30fps. Doesn't matter if they are hardcore gamers or not! We all have the same ability to see, certainly, hardcore gamers doesn't have any better vision than non gamers. The only difference is that gamers KNOW that the framerate makes the game smoother etc, wheras casuals also notice the difference but cannot put it into words.
I only have casual gaming friends in real life. We play Fifa and some CoD. Every single one of them (most of them dont even have consoles at home) notice that when we play Fifa (prior to Fifa10) on my PS3, its a lot slower and less responsive than playing it on the X360 at my friends house. They dont say that the framerate is shitty, because they dont really know what framerate is, but they certainly notice the difference. They might not comment on the difference, because frankly, they dont really care, but everybody is able to see it!
Similarly, its VERY easy to prove that casual spot 60\30 fps differences, 3d FX did this a decade ago, when they released a demo that rendered half the screen at 60fps and the other half at 30fps. Everybody with a working set of eyeballs saw that 60fps is more fluent. Case closed, casuals do notice difference between 60 and 30 fps.
The real question, is not if casual gamers can see the difference between 60fps and 30fps (they can, beyond any doubt), its if they prefer 30fps and better visuals over 60fps and worse visuals. That question however, is extremely difficult to answer, as framerate have alot of impacts aside from smoothnes of picture, that are hard to measure (responsiveness, how fluid the controls feel, etc), also how important the impacts of framerate is, will also depend completely on the game in question.
Nobody cares if Civilization runs at 20fps, but everybody would cry if CoD suddenly started to run at 20fps