It's true to say that the vast majority of bets in a race with a 1/3 jolly are on the favourite, but it's also true that the vast majority of bets laid are also on the jolly. That's not said in relation to this case, but just to point out the mathematics of betting.
Let's clarify one or two things here. This was not strictly a fixed race, merely one in which everyone expected a certain result (Ballyvoge was a genuine 2/5 chance on form, it's not like Dobbs has gone and won on a 50/1 rag!), and where the way the opposition were ridden was governed by their expectations. Michael McAlister didn't expect his mount to get anywhere near Ballyvoge, so he didn't plan in advance how to stop it. He merely found himself unexpectedly challenging an unwilling favourite in the closing stages. At this point, he's probably in a quandary ~ his horse isn't "expected" and everyone is cheering for Tony Dobbin so what does he do? In the end he panics somewhat and makes it look rather farcical.
This wasn't some race fixing scandal in any way and no-one was landing a coup. It doesn't really bring racing into disrepute, it's just a little silly. It does need to be addressed though, while the stewards should be wise to it in advance and give the jocks a talking to pre race "I know you'd all like to see Dobbin win, etc etc but this is a proper race and there's no place for sentimentality; if I think you haven't tried, I'll have your guts for garters..."