I don't feel anything should be nerfed.
The SM codex was the last in 8th, and only had a shelf life of less than a year.
We are getting a new codex for 9th soon, and other books will be released after. For all we know after a year or so the Astares will be the weakest army out there.
alternatively, if weapon stat leaks are any indication, salamanders' ignore AP -1 may be a lot more impactful 9th. GW may consider that an indirect buff since it means sallies aren't getting hurt by it while most of the other factions are.
Also add in potential fluff reasons; Salamanders are renowned for their resiliency and craftsmanship. They're also known for being very considered and deliberate in their actions. Getting rid of the hit re-roll may be intended to nudge salamanders into a less run-and gun, more slow and purposeful, playstyle, with the wound re-roll being deemed sufficient to show the superior crafting of their weaponry.
I suspect both those are factors in their nerf decision.