Good point about community. That's one of the things I really like about Scratch for the younger audiences (though I have also successfully used Scratch with adults as well!). Is there not much of a community with Python? I admit I haven't really looked yet.
For most people who want to learn to code they've experienced or seen something that has excited them in some way. This could be anything from a website, an iphone game, an error on their bank statement, or the tessellated feature on the side of a building. Someone who is excited by the visual feedback of a Processing app may not be excited by the simple high-level magic you can do with NLTK, or the funny things that you can do to a webpage in the developer's console.
That said, I've been following Processing since it's early betas and I think it's a fantastic first programming language -- not just because of the mechanics and ease of use -- but the fact that there is a giant community that fosters and encourages exploration in a way that humans can understand.