Wrong. Enforcement is done by the browser. Yes, a CA's certificate policy may govern how long a certificate they will issue. But should an error occur, and a long-lived cert issued (even maliciously), the browser will reject it.
The browser-CA cartels stay relatively in sync.
You can verify this for yourself by creating and trusting a local CA and try issuing a 5 year certificate. It won't work. You'll have a valid cert, but it won't be trusted by the browser unless the lifetime is below their arbitrary limit. Yet that certificate would continue to be valid for non-browser purposes.
