Why might Intern timeout with BrowserStack, but not Sauce Labs?

Edit: This has since been solved as an interesting network issue, see my comments and answer below.

Original Post:

My goal: Setup proof-of-concept tests on BrowserStack with Intern.

I went through the intern-tutorial, which all worked beutifully for me on Sauce Labs, and now I just want to learn what it takes to modify that configuration to test on BrowserStack, which keeps failing for me.

The terminal command, as per the tutorial:

./node_modules/.bin/intern-runner config=tests/intern

When running that, I get:

Listening on 0.0.0.0:9000
Starting tunnel...
BrowserStackLocal v2.2
Connecting to BrowserStack using WebSocket protocol...
Connected.
Ready
Error: connect ETIMEDOUT
  at errnoException  <net.js:904:11>
  at Object.afterConnect [as oncomplete]  <net.js:895:19>

TOTAL: tested 0 platforms, 0/0 tests failed; fatal error occurred

Environment:
OS: Mac OS X 10.9.4
Node: 0.10.29
NPM: 1.4.21
Intern: 2.0.1

Variables set in ~/.bash_profile as:

export BROWSERSTACK_USERNAME="<my_actual_username>"
export BROWSERSTACK_ACCESS_KEY="<my_actual_access_key>"

Intern configuration set in tests/intern as:

define({
    proxyPort: 9000,
    proxyUrl: 'http://localhost:9000/',

    capabilities: {
        'selenium-version': '2.41.0'
    },

    environments: [
        { os: "Windows", os_version: "8.1", browser: "chrome", browser_version: "34.0" }
    ],

    maxConcurrency: 3,

    tunnel: 'BrowserStackTunnel',
    tunnelOptions: {
        verbose: true
    },

    loader: {
        packages: [ { name: 'app', location: 'app' } ]
    },

    suites: [ 'tests/hello' ],

    functionalSuites: [ 'tests/functional/index' ],

    excludeInstrumentation: /^(?:tests|node_modules)\//
});

As in, this is all that has been changed since the completed tutorial:

• Removed all but one environment object (for simplicity), modified it to a format supported by BrowserStack.
• Set the 'tunnel' property to the appropriate tunnel class.
• Set tunnelOptions: { verbose: true } for debugging.

Things I've tried:

• Setting BROWSERSTACK_USERNAME and BROWSERSTACK_ACCESS_KEY inline on the command line when executing the runner, just in case.
• Used the configuration here (which I recognize is out of date): http://stackoverflow.com/questions/23304388/intern-js-and-browserstack
• Stupidity checks, computer reboots, etc.

My environment object should be valid, as its based on one coming back from:
https://www.browserstack.com/automate/browsers.json

I feel like there's some basic thing here I'm missing about the configuration.