G'day Ash,
I know from you're earlier post GH Jnr is not your fav person, but that aside, there is a push out rule for a couple of reasons..to give all horses a chance and reduce the griping from the punters about "the trotters always get boxed in". It has been about for quite a few years, in NSW since around ther mid to late 80's if my memory serves me.
Before that it had been in existence in New Zealand for decades! I remember as a kid watching Phil Coulson pushing out from the rails and winning the 1971 Christchurch Inter final on Junior's Image, brilliant drive!! Subsequently lost the race to Stella Frost ( Doody Townley)due to a hotly disputed but nontheless upheld positive swab.
I can tell you from experience, if the inside horse has a head to neck advantage over the outside horse, he will usually succeed in getting out, if the outside horse has the same advantage you are hard pressed to budge him, however if the two horses are level, which ever horse is going the strongest will have it's way, if the outside horse ( in this case Dasher VC) had a bucket full of petrol in the tank he would have held his ground.
I am neither a fan nor a detractor of GH Jnr, but I enjoyed watching his drive... there are some who attempt this move and cause havoc because they try and run out at 90 degrees, I thought he caused as little interference to the other horse as possible while giving his own horse every chance within the rules..doing his job I'd call it.
Cheers,
Dan