It's not (just) that you have to use WebKit...
It's that the version of WebKit available to use in apps (or competing browsers, which are mostly just a skin on WebKit on iOS) is not as up to date.
Or, at least, that was the case when I was doing webapp work at $JOB-1.
The APIs we needed were (recently) supported by Safari (and iDevices kept Safari up to date so we didn't need to worry about that), as well as on any recent Chrome, FF, or Edgium.
They weren't available on the older WebKit engine used by anything other than Safari.
We had graceful degredation, but did have to explain to some clients they'd need to switch browsers to see the features we were trying to demo!
Biting the hand that feeds IT
