Really low drag-coef, and small frontal area means less hp needed to go faster. Top speed is rated at 143 mph ... all without grenading a driveshaft.
The Subaru limited number is probably true as it's based on what Subaru North America ordered. The factory is making ~100,000 units but Sub NA only believed they could sell 8000 or so. Ignoring the hype and the initial surge of sales, you don't want another RX-8 for the next 3 years.