I remember when Scion came out. xA, xB and tC. If I remember correctly, the whole deal was to aim at the younger generation, but many people liked the cars, functionality and simplicity that it caught on to the older crowd.
What I also want to say is that Kei car and boxy small cars "looked" JDM, so when the xB came out, Toyota knew that people were going to build them (at the time Honda was the dominant platform to build).
I personally felt the xB (Toyota BB) was the big seller because of that "bold JDM look". The xA I did not see build as much and the tC is a good platform as well.
Today, 2015, I feel that they have kinda kept up with that demographic with the FR-S model.
Some of the best forums ( I'm sure there are others)