I can speculate this can actually attract even more of the target audience to you. Mac people probably feel more enthusiastic about Mac-specific software announcements and are steadier to go and take a look at something Mac-specific than at yet another generic browser. And for the conversion rate - this probably even is a serious boost.
And those enthusiastic about Mac, also care about things like how 'macOS' is written. Attention to detail matters and shows your own level of dilligence.