You can also add in this aspect.
The models that you see in most tickling videos are cast for specific qualities, namely being more ticklish and having greater reactions to tickling. This produces something not unlike the 'porn distortion' that vanilla porn has. You are not seeing average reality in videos but extreme ends of it that satisfy the medias audience goal; to get off.
Most people respond like you describe in your first paragraph. Moderate responses, more movement than sound, and so forth. That is the average human response. And if you tickle a lot of people over your life you come to see it and understand it. Yes most folks are ticklish somewhere, but often not screaming ohpleasestop unending laughter ticklish. If most of ones intersection with tickling is videos, its easy to get a somewhat distorted view of 'normal'. Which is also there same problem that vanilla porn produces on its audience too.
Myriads