The fact that 76% of folks have not even tried sport mode speaks nothing to it's quality. If anything, it says those folks are happy with offline single player play, private rooms, or photomode (or like many games, have bought it but not had time to play or are into other games right now).
As far as the criticism of the poster who said he tried the beta and demo and decided not to buy, you can't say his opinion isn't valid because he didn't invest "enough" time, or that he "didn't really play". On the other hand, the poster seems to have missed the point sems4 was making in that he didn't think he would like it that much at first and now after X hours he's had a change of heart.
So in my mind, the point that isn't being touched here is that sems4 (and others who posted similar to him) is possibly pointing out that for some folks who dismissed the game at first as garbage or unenjoyable may be wrestling with past expectations and indoctrination (for a lack of better word) with past GT formats, and that given more time one may be able to move past that and come to appreciate it for what it is. This type of thing occurs in all forms of media. Movie and TV series, bands/music, books/authors. Not saying that it will definitely happen or that rejection to change is somehow wrong (everyone must make their own choices of what to invest time and energy in), just be aware (by listening to others experiences like sems4) that initial opinions can be misleading or coloured by lots of things going on at the moment and sometimes it may be worth a second look.
I have had this happen countless times with various media where after coming back to them much later I find that I actually enjoyed them.
Anyway, that's my dollar and change.
Have a great weekend y'all.