Most technologies I use have a single interface to them. That's largely the way things are developed. But one of the things that is happening on the web is that services are developing multiple interfaces.
And I like having multiple interfaces to a service. I like being able to use Outlook, and Entourage, and webmail, and blackberry to manage my mail. Each interface allows me to do certain things better.
This is also true with Twitter. I access Twitter via sms, mobile web, and Tinytwitter on my phone, via the web, Twitterific, Snaz, and Snitter on my desktop. Each interface is better for certain things. None would get the entire job done by itself.
I use a voicemail transcription service called Simulscribe. It takes all the voice mails I get on my cellphone, office phone, and home phone, transcribes them, and sends them to me via email. Recently they offered a mobile app that I use on my Blackberry. And they are working on a desktop app and an outlook plugin. I think they should open the api and let a thousand clients bloom.
Because having multiple interfaces into a single service is a great thing.