In terms of acceptance after check-in closure time this is bound to be inconsistant, but not due to different airlines neccesarily but each individual circumstance operationally.
As you know there is a lot that goes on behind the scenes in order to 'turn' an Aircraft, you might turn up late on monday but the A/C is running slightly late in which case the dispatcher has not started/filed his/ her paperwork so you may be accepted.
Then you turn up late on tuesday at exactly the same time with a different airline, but the A/C was in early and everything is done and ready, as soon as the check-in closes, exact male/female/bag breakdown will be used to FINALISE the loadsheet, in this instance the dispatcher probably wouldnt do an LMC.
To you that would understandably appear inconsistant, but there is a reason for everything that happens.
The only thing that impacts on acceptance after 'positive close out' from a different Airline perspective, is certain low-cost carriers, you know who you are ha ha, wont accept pax who are late under ANY circumstances in order to get you back to their ticket desk and buy another ticket.
As for other Airlines charging a great deal of money on the day, well thats just business im afraid, you need to get somewhere and they can offer you a seat, in short you need them more than they need you, so they charge accordingly.
I suppose the only way to make it consistant would be a uniform all airline policy of zero tolerance of acceptance of PAX after closing time, personally I would rather it appear inconsistant, the amount of PAX who are accepted when they have no 'right' to be has always amazed me, as it creates much more work and stress, but circumstances dictate you wont always be that lucky.
