I'm not really following what you're saying. I believe you're making my point - if you are in Apple's ecosystem, you're in. And it is popular. But Google provides search and email and maps and contacts for "everyone." That's why when they actively blocked Windows Phone from their services, it was anti-competitive.
Other entities like Instagram were under no obligation to build for Windows Phone, but 6tag was built and served the purpose. I don't believe Instagram blocked 6tag from working. If they did, it might not be anti-competitive, but just anti-consumer.
Beyond this, Google's behavior had ripple effects. Developers could tell that Google was putting up roadblocks to make Windows Phone an undesirable platform, and that discourages contributions.
If iTunes only exists on iPhones, but not Android, then it doesn't matter if it also doesn't exist on Windows Phone. Apple, the iPhone and iTunes are not monopolies. They are a walled garden, though. That's just a separate issue.
Other entities like Instagram were under no obligation to build for Windows Phone, but 6tag was built and served the purpose. I don't believe Instagram blocked 6tag from working. If they did, it might not be anti-competitive, but just anti-consumer.
Beyond this, Google's behavior had ripple effects. Developers could tell that Google was putting up roadblocks to make Windows Phone an undesirable platform, and that discourages contributions.
If iTunes only exists on iPhones, but not Android, then it doesn't matter if it also doesn't exist on Windows Phone. Apple, the iPhone and iTunes are not monopolies. They are a walled garden, though. That's just a separate issue.