From a UK persepctive, I'm not sure where you will find 'official information' on the subject, but all the ATCOs I know will tell you that the -5/+10 belongs to us for some of the reasons you have stated among others.
It's not easy for us to get an aircraft off the ground dead on time, so we are allowed a tolerance by flow to enable us to get the aircraft airborne. Crews know this but are reluctant, probably due to economic pressure, to delay flight plans in case they get a CTOT which can up to 3 hours later than their planned EOBT. However, this is not our fault, as we in ATC have to work within the rules. A handling agent (at least at the airport I work at) is responsible for informing the flight deck of any CTOT. The flight deck should then keep the handling agent informed if they can make the slot. If not, then the flight plan should be delayed.
We don't make the rules, but we have to stick to them.