Consider the tremendous difference in R&D effort spent refining the piston engine vs. the rotary, both in terms of $$ and decades.
It's really quite amazing the rotary can compete at all. And equally amazing Mazda has stuck with the rotary when the easier path would have been to abandon it entirely.
The combination of increasingly stringent emissions laws and increasing fuel prices are going to make it tougher to keep an alternative technology competitive. Let's hope Mazda finds some real breakthrough rotary improvements.