The Mishnah Berurah (215:20) brings from the Chayei Adam (Kelal 5) and Pri Megadim (Pesicha LeHilchos Berachos) that even if there's sfek sfeka (a double doubt) telling you to make a blessing, we don't rely on it to allow you to make a blessing.
In contrast, I heard in a class that there are poskim who hold that if the majority of factories in a country are owned by non Jews, you can rely on rov for tevilas keilim and make a blessing. This includes Rav Moshe (OC 3:4).
Are the opinions who say this by tevilas keilim disagreeing with what the Mishnah Berurah brings? Or is there some distinction I'm unaware of.
I ask because there are those that say (such as Teshuvos HaRashba 1:401) that sfek sfeika works through rov, by looking at the majority of possible outcomes. Not everyone agrees. So would that be the distinction? It might be that the Mishnah Berurah doesn't distinguish, as in the Beur Halacha (60:4 s.v. וכן הלכה) he explains that even though the halacha is mitzvos need kavana (which I'm understanding because of rov, but you could argue), for blessings we still need to be cautious for the (minority) opinions that mitzvos don't need kavana.