They use the on-premises version, which is much faster: https://jira.atlassian.com/secure/Dashboard.jspa
I'm actually going to look into shorting Atlassian now.
a) the public facing jira.atlassian.com is Server/DC instance - but this instance is only used for customer/outside world facing tickets (I think)
b) internally for our own development we use a few (several?) cloud instances -> but I can only speak to those I interact with (Conf Cloud and Jira Cloud primarily).