A small amount of people own IS F's, while an even smaller number actually make it to a forum to discuss anything. From what I've experienced, the majority of those people who do, post when they have issues, general questions, etc. to be asked, as opposed to posting any significant or new information. With a deeper aftermarket or a car which was more affordable/popular in standing among enthusiast, say cars like the Miata or M3, you'd probably see both a bigger following and more activity.
I'd say this is par for the course, so far as a relatively new car is concerned, from a brand trying to shift its image. It takes time (years) to build that fanbase.