One is a shoulder to the head of an upright player where the forearm comes through onto the head as well, the other is a straight forearm to the head of a player lower down as his knees are bent. In the first case, the defender also jumps up off the ground to make contact.
Prior was rightfully sent off for his mistimed, malicious and terrible tackle.
The same should have happened to Inglis.
As far as the suspension goes, you weigh the two up against each other .. and there were parts of Prior's tackle that were worse than Inglis', but also parts of Inglis' tackle that were worse than Prior's (such as jumping into the air to hit dangerously and with intent after he had at least 3 seconds to decide how he would tackle the player coming towards him).
As such, I would say a roughly equivalent suspension is the right outcome .. however, I think Prior should have copped 10+ like Travis Burns, which is why I think Inglis also should have copped 10+. Given Prior only got 5, Inglis was never going to get more than that as it is an equivalent tackle on balance.