The advantage of Twitter isn't in using it as a substitute for email, it's in its ability to kickstart unexpected conversations and get people talking with a very low barrier to entry. When you have an indie outreach guy on twitter, you have someone who can hear about cool new games from reading their twitter stream, or who can pop into ongoing conversations with indie studios, or who can ask for feedback and start a big public discussion about the strengths of their platform.
In this case, Twitter's standing in as a proxy for public communication in general in part because Nintendo has so few routes for such communication that dropping this one route is a pretty significant loss.
It's working much better than it did last generation, certainly. It's not working anywhere near as well as Sony's comparable push is, though, which indicates that there's still room for improvement.
It is good to see individual developers seeing some success on Nintendo's platforms this time around (again, very much unlike most people's experience on Wii and DSi) but it's still limited primarily to devs who target eShop for timed exclusives. Getting to the next step in terms of building up indie support is going to have to involve bringing in more of the PC indies, and that's very difficult to do without real, ongoing public communication.
This is like the generic head-in-the-sand position. "All those people complaining must be part of an insidious conspiracy!" No, it's just people complaining about stuff that comes up while they're doing their jobs. If you look at the things Microsoft, Sony, and Nintendo have broadly been taken to task for over the last ten years (by press, developers, or consumers) very few of the most major complaints are unsupported and almost all of them are things that the platform-holders went out of their way to remedy later on down the line.