This isn't really a surprise, because as Pichai said, it's "in Google's DNA... to be universally accessible." Google has already ported a ton of apps to iOS, and Google Play Music All Access is simply the next one to make the leap. It is telling though that this move didn't happen until after All Access was launched. We can't say for sure, but we suspect this means you won't be able to purchase music or maybe not even subscribe to the $10 per month service through the iOS app, because then Google would have to give 30% to Apple.
More likely, the app will only give users the streaming music and any music you may have in your Google Music library, but no purchasing options. But, that's just an educated guess. We'll see for sure in a couple weeks. Pichai said it will come to both iPhone and iPad, but didn't mention if the iPad version would be optimized or not. We'd guess not, since both the Google Maps and YouTube apps are still not iPad optimized yet.