Yahoo Mail, Hotmail, and my own personal mail server can all interoperate with Gmail as first class citizens. I can easily send an email from Gmail to someone using Hotmail. That's how Gmail was able to easily get a foothold in the market, because Gmail users could email users of other email providers.
Identica, other StatusNet installations, and other services cannot fully interoperate with Twitter as first class citizens. How do I send a Tweet from Twitter to someone using Identica, for instance?
Gmail isn't open source - Open APIs/Open Data is not Open Source. People use the Gmail service they allow external integration to broaden Gmails reach/ecosystem - this makes the Gmail service more attractive.
The fact is they'll never Open source the Gmail client which is their secret-sauce/USP that others are looking to replicate. Like twitters application platform, that is not something anyone should ever expect to be given away - its bad business.
Twitter isn't open source either. In that way they are similar to Gmail. Twitter is also headquartered in the US, same as Google. There are innumerable other ways that they are similar.
There are also some major differences, such as the one I described about interoperability. Another difference: unlike Gmail, Twitter's "secret sauce" isn't their website. It's their walled garden social network. Twitter could open source their whole website's code, and it wouldn't much help anyone build a Twitter competitor. StatusNet is already pretty nice.
Also, since we're veering way off topic here, note that I am not arguing that Google is "OSS's best role model", like you said about Twitter. I'm just using Gmail as an example to illustrate how Twitter's walled garden is different than how email works.
The word is federated. Email is federated. Google Wave was federated. Twitter is not federated. You can run your own email server and be a first class citizen in the network. You can't run your own Twitter server and be anything but a layer on top of the Twitter API.
More importantly, federation is inherently decentralized. If GMail goes down, your email server still runs and still inter-operates with the rest of the world.
Yahoo Mail, Hotmail, and my own personal mail server can all interoperate with Gmail as first class citizens. I can easily send an email from Gmail to someone using Hotmail. That's how Gmail was able to easily get a foothold in the market, because Gmail users could email users of other email providers.
Identica, other StatusNet installations, and other services cannot fully interoperate with Twitter as first class citizens. How do I send a Tweet from Twitter to someone using Identica, for instance?