I don’t think that’s common for any brand, including Siemens. When I tried the Rexton (a Siemens brand) at Costco I got a 36 month warranty. I assumed it came from the factory.
This is not really relevant but when I was trialing the Rexton Insite I accidently dropped it in a full glass of water. It took a couple of tries to fish it out of the glass. I took the battery out, rolled up the end of a piece of TP, and stuck it in the battery opening to try to wick away any water I could. Then I put it in the dryer (an open top Audio-Dry) and the next morning it worked fine.
I had one hearing aid that went out, a Starkey Destiny, just after the one year warranty expired. They fixed it for $140s and gave me a 12 month warranty from that point. They said it was caked with wax although I don’t see how that would actually damage it.
Anyway, I clean mine every night now (Resound Future), and brush the dried, flaky wax off the receiver end every morning after being in the dryer all night.