Earlier this week, we reported of a petition going around the Killzone.com forums which was asking for a party system to be implemented into Killzone 2. This morning, we received a response from Guerrilla Games Senior Online Games Designer, Erik Boltjes.
In response to why KZ2 is lacking a party system/ playing with friends:
"Hey guys,I totally agree with you; we should have a friends-party
system. Unfortunately due to reasons I cannot go into here, it isn't
as easy as 'just implement it!'.