There are a million things relating to an attack which the IRCd has no bearing on whatsoever.
Not quite right but you are close. The hardware, the software, the connection quality and size and the admin's skills all play a role however it is only IRCd's we are discussing so to the maximum effect possible in this thread I am correct.
No-one makes money from IRC, though some organisations use it as a value-adding tool for their broader product range. The notion that freeware coders pay more attention to security is a lod of bull too. You are forgetting something here - the coders of commercial products are using that was a means of putting their daily bread on the table. Are they going to jeopardise their livelyhoods by being slack in that important area? I think not.
In reply to Monosex: CR and MS Exchange are two commercial products but there's others, IRC Plus, Chatspace and Rooms, all of which offer 'enterprise' versions costing alot more than what I am used to.