There are already countless websites abusing the web notifications API to push spam to end users. You're probably savvy enough to effortlessly avoid it, but the average end user often is not. We can't keep ignoring the the UX issues with a lot of these web APIs if we want them to be successful. Users don't care to philosophize about the open web, they just want their shit to work. That's what Apple iOS is providing them, and they will continue flocking to iOS until they're presented with a better alternative.