The old time rule that leather is best is getting challenged by the new textiles. Vanson now has a textile suit that is approved for racing. As the textile suits get better and better it will get to the point that they get acceptance, even from the old guys. As it sits now, a GOOD textile is acceptable for street riding.
I've got a textile suit because it is way more practical, and a little less expensive. The textiles are lighter, waterproof, and cooler, making it easier to wear protection ALL THE TIME. The best leathers in the world are no good if they're such a pain in the ass you don't bother putting them on.