I'd expect an organization who pays for the service should have access to their data in it. If you fear the change, you really fear the people who are or will someday become a service administrator. If you fear that, perhaps you should consider if you're really happy where you are. I'd suspect you either have trust issues with your corporate or IT management, or you work at a place that moves too slow for IT to have anything better to do than troll through private chats.
In many cases, IT can already do a lot of other things like span your port, read your e-mail, shadow your terminal, capture all printer output, etc. But in practice, this kind of permission is usually used when someone is stuck and an employee unreachable or out on vacation, or an employee is terminated and you need some critical piece of information they might have in their chat history.
I pay for the service for my company. I trust my employees. I don't want them to think I'm snooping on their personal conversations between each other.
You also control the routers, the email server, any other form of digital communications, and possibly even the software in their desktop.
What's the difference? Just because an employer can snoop -- and might be legally obligated to snoop -- doesn't mean your company can't have a clear policy regarding when and how you will exercise that ability inherent in owning infrastructure.
Well most of the team is remote and we use Google Apps which doesn't allow email access (as far as I can tell, at least not without changing passwords and a few other tricks).
There is a difference between having a feature which allows someone to view your private chat logs (something Google Apps doesn't have) and what it sounds like HipChat are implementing - though maybe they're going to make it just as difficult?
In many cases, IT can already do a lot of other things like span your port, read your e-mail, shadow your terminal, capture all printer output, etc. But in practice, this kind of permission is usually used when someone is stuck and an employee unreachable or out on vacation, or an employee is terminated and you need some critical piece of information they might have in their chat history.