In my experience, most people who ride both started with motorbike trials and got a biketrials bike second. I did, my mate did, my brother did, my other mate did and his uncle did. I don't know anyone who rode biketrials first! You got that totally backwards, it takes just as much skill, if not more to get over the same obstacles, and on a push bike you just get off and try again when you get stuck, with a motorbike, you can't get out of tricky situations easily at all.