It is needed because of the highlight-only annotations.
In this case we want the annotation.quote to fill the remaining space besides the link and without this it's not looking well.
I'll show you.
It looks like this with the "no-overflow" class
![with_no_overflow](https://f.cloud.github.com/assets/2094134/871324/a74569ae-f846-11e2-9588-f829d7110f53.png)

But without it:
![without_no_overflow](https://f.cloud.github.com/assets/2094134/871325/af85403a-f846-11e2-9134-a8de4988e9da.png)

This will (or may) change after the common stream redesign.