Many Android phones don't have notification LED either.
Notification LED is a classic solution during the feature phone era for notification, in the era where notifications are either calls or SMS, only.
Today, notification can mean a lot of things, from emails to apps, etc. Even if you allow color differentiations, it's not intuitive anymore for the lay person. The ideal solution would be an always-on part of the screen that indicates notification (will be possible when Apple transition to OLED). Many Android phones headed this route, and Imo it's the better solution for the modern smartphone than a blinking LED.
Of course, there's the wearable solution as well. I don't miss notifications anymore ever since I use my Moto 360 with my Android phone. I get notifications even when I put my phone in my pocket/bag. Much better than a blinking LED that you will only notice when you look at the phone.