The framerate being lower doesn't magically induce sickness while it being higher doesn't. I'll buy the eye-strain deal, but not movement sickness.
Really, you know how my body works?
Seriously, you can tell me what is causing me to get motion sickness and what doesn't without seeing it?
I've played games, before I improved my system, with their highest settings, so I can see all the picturesque views (Farcry for this example). I was getting between 27 and 35 FPS. I'd get sick after 30 mins. I took a lot of breaks and kept returning after the sickness would go away.
Eventually I tried lowering the graphics settings so I could maintain over 40 FPS. All of a sudden I could play for at least an hour without feeling sick. I then tried the same thing with every new game I got. Sure enough, when I had FPS in the 30's, I would get motion sickness from 30 mins to 60 mins of play, when I had 40+ I could last over an hour, and with over 50+, I could play all day long if I wanted. (I may notice an ever so slight tenge of sickness if I play for a long enough time, but nothing really uncomfortable).
The same issues occured with Morrowind, Oblivion, Crysis, and just about any game where I controlled movement with my mouse. It seemed a lot of MMORPG's I played didn't make me sick when I used to keyboard turn. As soon as I played those same games with the mouse, I had the same issue.
After learning what affects me, I convinced some friends of mine, who refused to play 1st person shooters for the same motion sickness issue, to try using lower graphical settings for more FPS. Now they can play 1st person shooters.
Count yourself lucky.
You may be fine playing with low FPS, but you are not the only person, it is different for other people.
It's just not acceptable. 
