Wow, you are blind by your homerism.
In either scenario, the player getting hit didn't have the puck. The only reason why Marchand got suspended was because Salo got injured (and I'm sure there was a lot of squaking from our management team). Had he have gotten up, like Marchand did, Shanahan wouldn't have even watched it twice.
You are also forgetting that earlier in the series Marchand had made a couple of low bridge hits like that on the Sedins and others. He was not penalized for those plays whatsoever. So later in the series Raymond repays the favour, by ducking on a player known for dirty and dangerous hits, who was coming at him with speed. In that instance, it was a justifiable hit. Also it was from the front.
Salo's hit was in the regular season many months later, on a player who wasn't even going for a big hit, who didn't expect to get low bridged from BEHIND by Marchand. See the scenarios are different.
That's not homerism. That is just how it was. And I hate to use the NHL ruling as an example to prove my point, as they are inconsistent and poor at their job, but I feel it actually does matter in this instance, as they saw the two hits as different.