That's half-true. No adults I voluntarily associate with care what brand of phone anybody else has in theory, but a lot of the iPhone owners are vehemently unwilling to install any third-party messaging apps. That means:

• Messaging about anything where security is important is a problem. Most people don't have big secrets, but sending things that could be used for identity theft isn't terribly rare.
• Exchanging high-quality media is impossible.
• People will exclude non-iPhone users from group chats because falling back to MMS is a bad experience for everyone.