Most residential internet connections don't have any sort of DDOS protection, so privacy issues aside, at the very least you are open to a simple denial-of-service attack. This was a huge problem for the popular progamer "Destiny" in the Starcraft 2 community.

So is it also really scary that the mods/admins on the Starcraft 2 forum could also see his IP address?

The risk of being DDOSed when you share a contact on Skype and they find out your IP address is hyperbole.

There is a pretty substantial difference between a few Blizzard employees knowing your IP address and the entire public knowing your IP address.

You obviously don't live in China...