This is my understanding of the situation too. Combat logging (or something similar) happens in most if not all multiplayer games to some extent, but judging by the comments on this forum it seems to be a particular problem in ED - and we need to ask why. At a fundamental level, I have to suggest that it is a symptom of a general lack of respect between players. I for one wouldn't consider such actions as remotely appropriate in other games I've played - and not because of possible penalties but because I actually care about how other players see me. Clearly at least part of the blame for this lies with a poorly-designed game mechanic which encourages random unevenly-balanced encounters between players who may never meet again, but I can't help feeling that the attitudes expressed by some open 'regulars' on this forum have also played a part. I'll not provide specific examples (it would be unfair to cherry-pick, and I see no reason to assume that those commenting are by any means to worst offenders), but when one sees statements to the effect that any newcomer getting 'ganked' or harassed in open deserves what they get for playing there in the first place, it isn't difficult to come to the conclusion that respect - and consideration - is lacking. Maybe FD can come up with something to deal with the worst offenders, but ultimately if the open player base wants a better environment - one where people don't combat-log out of self-respect, and respect for others (as I've seen in other games) - they need to look at broader behavioural issues, rather than venting yet again on the same subject while ignoring the root causes.
In most MMOs if you loose connection or log out in combat situation, your character stays online for a some time. They may die, they may survive, this depending on the game and circumstances. But in most games death penalty is not really very harsh. You may lose some XP, get your armor damaged etc. but in general you respawn in some safe location without the whole thing having much of an impact on you. It can be a bit unpleasant, but in general you're back at where you were a few minutes before in terms of your ingame progress. You won't have to grind for hours to get back where you were.
In ED death is much harsher. Especially for a trader, flying one of the big freighters. If you loose Type 9 with cargo, it can really hit you. Yes, usually you will have enough money for insurance and new cargo, but every loss means you will have to spend another hour, or two or three just to rebuild what you've lost. And there is a significant chance you won't survive your next hostile encounter either. So it can become not only a tedious activity for a game you're supposed to enjoy, but also fairly pointless. I have no doubt there are some people who enjoy trading and it's their thing, but in most cases trading is just a way of making credits for other purposes, so each death in space forces you to grind more.
I was extremely lucky when flying my Type 7 and somehow I didn't get interdicted by pirates for some 60 milion credits, mostly due to doing a short run between fairly secure systems. Loosing that ship even once would mean a loss of about 5-6 mil and in that run I was making about 2mil per hour. So the possibility of getting interdicted was really dreadful. Those ships are designed to be either a prey for pirates or to fly in convoys. The problem is: there is really no reliable way to fly them in convoys. You could get some players in fighter ships to accompany you from time to time, but finding somebody who will tag along your space cow day in / day out isn't really an option. I only hope that Frontier finally adds NPC wings, because otherwise the only solution available is to switch to some warship (which I did as soon as I could).
So I am not surprised if traders do log out when it gets hot. Can't really blame them. I don't usually play in Open, but if I were flying a Type 7 full of cargo in Open, the only thing that could prevent me from combat logging would be roleplaying.
I don't think combat logging has anything to do with the crime and punishment system in Elite. Who cares if the pirate gets high bounty on their head or if they are immediately hunted down when you've just lost 20 million? The only things that could be an incentive for players not to combat log is either to survive each hostile encounter, so no PVP mode, or to have more options to protect themselves effectively (other than buying a warship). You can't really enforce punishment for combat logging (and Frontier won't do that, combat logging is a relatively unimportant issue, as in: it's hard to blame them for that), so if there is no stick they can use, they better think about some carrot and convince more players to stay online when in combat, even when loosing.