On the raising side, you're absolutely right. A custom URL scheme generally captures what you want to do (i.e. the intent) not how.

On the handling side, however, on iOS there are limitations that I think make them qualitatively different:

- only one application can handle any given URL scheme

- no mechanism (other than Apple apps win) for choosing between apps that want to handle a URL scheme

- no notion of optionally handling a URL scheme based on its contents (which enables very useful filter-like behavior)

- no notion of "returning" to whatever raised the request (there are schemes to hack around this, but they are limited and brittle)

- built-in support for carrying general payloads (rather than having to encode them in a URL)

There is overlap. I hope HTML5 will dump registerProtocolHandler() and extend Intents API to use scheme in addition to MIME type.