You're right: I made a mistake; blurring would occur with fast movements at slow shutter, not low fps. Problem with low fps is the lost of information.
But I disagree when you said: "The 30/25 fps were important in the analog age, whit limited resolutions viewing small areas. In the megapixel age, fps are not so important because your monitored area is bigger."
Since the time-lapse age, it was determined that, for security proposals, at least 5 fps is enough to not loose any important information.
I remember a video from Pelco showing a line of people passing by a table with an ashtray on its top.
At 1 fps, suddenly the ashtray 'disappears' and you can't know who took it because it happened between frames.
But at 5 fps you can clearly identify who took the ashtray.
Therefore, to detect quick and suspicious movements, doesn't matter how big or small is the area nor the quantity of information (resolution) you're recording, but the quantity of movement (fps) is being recorded.
Someone remember and still have this video? I've been looking for it to show in my trainings.