How do some people RT (twitter) with more than 160 characters?

Sometimes I see people retweet someone whose original tweet was 139 characters, so when they add the @YourLongTwitterUsername it’s then, like 162 characters. But it still shows up (in Brizzly…) in full, although Brizzly won’t let me RT like that. What’s up with that, and how do I RT when the original is long?