Google may decide that it's worth losing a bit of feedback from Apple devices because of the competitive advantage that Apple's awful maps give them. They will still get plenty of feedback from Android devices, which massively outnumber iPhones anyway. And their maps are so far ahead that making their maps 110% better than Apple's instead of 100% isn't worth losing the opportunity to watch lots of Apple users jump ship and head in their direction.
And people will definitely be put off iPhones by the new maps. I am an Apple fan through and through but I would have looked around if I weren't an iOS developer. Lots of people rely on the maps app, strange as that clearly seems to some people on these forums.
I think there are plenty of people who are overreacting to this as well. Not saying the maps app is where it needs to be but to completely switch platforms over it is a bit drastic.
I also think you underestimate the number of iOS users. We aren't just talking iPhones here - there are over 400 million iOS devices out there. And Apple has a much better customer retention rate than Android so the number of Android activations while higher than Apple doesn't as accurately indicate the number of Android users.
Like others have said, there are alternatives. maps.google.com bookmarked works well plus Apple will continue to update the maps as crowd-sourced data comes to them. It'll take time, but it needed to be done.