This has been entirely unintentional. It just happens to be very handy to have a single destination that gets updated frequently throughout the day.
Part of this accidental dependence is the result of good design. Google Reader devotes most of its space to the intended content (news, blogs, headlines, etc...).
It makes liberal use of AJAX to make the UI incredibly responsive.
It even has keyboard shortcuts though those haven't grown on me yet.
They've also got several nice bundles of content that make it easy to find interesting articles.
It even plays nice with mobile phones that are not the iPhone. It is hard to overstate how amazing it is that Google Reader works with Pocket Internet Explorer 5! Nothing works with Pocket IE5 except sites that assiduously restrict themselves to whatever meager fraction of WAP-friendly HTML is grokked by Pocket IE5.
Not only does it play nice with Pocket IE5 it even makes other sites play nice with Pocket IE5 by stripping away all of the HTML goodness that PIE5 can't deal with.
I'm not sure I could go back to standing in line without Google Reader on Windows Mobile (or something like it).
Today I discovered that they didn't forget their "raison d'etre". The convenient search bar at the top of the Reader homepage searches, among other things, any of the articles you've ever read in Google Reader! So it's a great way to track down that handy link about something or other you read a while ago but forgot about.