While linking to other apps in Android is absolutely trivial and mostly painless (even considering it's java), the more tedious part is to implement the intent service itself. The "<a href=" example is the wrong one, since the call itself is practically a one-liner in java, whereas implementing the equivalent of a "Hello {{name}}, how are you since {{last-visit}}?" response would cause a hell of a lot more headache.

The API is solid though, the linking is done at a very low level, and to be honest when you get the hang of it, it's hard to let go of that awesome feature of the OS. I strongly support the use of RESTful IntentServices and ContentProviders, even if you don't open them to other apps, it's specifically the part that the Android OS got right. Opening them up for other apps to link to is a one-liner config change afterwards.