How to steal from Heroku

I love Heroku. I especially love their sign-up process (give them your email address, click a verification link and you're ready to go). No captcha. No SMS verification.

What stops someone from buying 1,000 email addresses, and hiring someone to create a 1,000 Heroku accounts? You get up to 100 MB of slug space to run code and host static content.

Does Heroku not care about this sort of malicious behavior? If so, why do they not care?