So you mean that GHash.IO are could be causing more orphan races than usual, rather than winning more orphan races than usual? Or both?
Am I right in assuming that this is only an issue because they have such a large chunk of the pie?
I think it's both (causing and winning), because of large chunk
separated from badly connected to the network.
It was similar when ASICminer had a big chunk in a single location with good connectivity - GHash.IO have it in few with bad connectivity, so the problem appeared a bit earlier.
There should be no single entity with much power (no more than 25%), but there is also another reason causing the big number of orphans - the rate is 9.63 blocks per hour, which is also 30+% over the normal rate for the network. Once it drops below 20% the things will normalize.
I'm not quite following you there - BTCGuild has had well over 30% of the hashrate at times and has not caused similar issues.