How could there be 7 replies and 0 views? Are the counters updated only so often?

Yes, that's been a feature for several versions now. Continuously updating the ibf_topics table to increment the views column on busy boards can cause the table to get locked. So there's a setting to only update this every few hours.

Every 1 hour I think it is. Otherwise if you made a mySQL query to update that tiny number for every visit on a forum this popular, your dB would crash.

I think that's been in there since 2.2.0 or 2.3.0 I cannot recall.

What's the performance gain?

Michael and Peaches have it right on performance gain.