These types of issue are always contentious, I suspect in no small part to the fact that there are 2 somewhat competing schools of thought.
The first being that there will always be an, albeit small, hardcore group of cretins that love finding ways to hurt themselves, and those around them. As such, and if for no other reason than protecting those around them, legislation is required to limit the likelihood of them doing this.
On the flip side is the argument along the lines of "why should the majority of the people have to essentially be penalised on account of the odd cretin".
From my point of view they are both valid points.
Inevitably, the people that the legislation is put in place for are the very people who will likely ignore it, so does it help?
Another issue, leaving aside the contractual legalities (as I think they muddy the water) and the profit-maximisation, is the fact that in an increasingly litigious society companies need to protect themselves from prosecution as a result of the stupidity of others. So weighing up the trade from selling LPG to motorhomers and people with gas take-off tanks (as opposed to LPG vehicles with liquid take-off tanks) against the severity and likelihood of an 'event' may lead them to the conclusion that the reward is not worth the risk, or if it is that they need to put in measures to protect themselves from prosecution on safety grounds.
Stepping away from the specifics and looking at all people individually, there is a phenomenon known as 'risk-compensation'. The theory being that individuals have a fairly well set acceptable level of risk. These will obviously vary from person to person. Increasing the safety of a task/item/situation generally leads to that person taking more risk.
A couple of examples i've used before are the HK armed police issuing full body armour to their officers only to find the number of gun shot wounds and fatalities increased (as a result of the officers taking more chances). A rail crossing that had cars speeding across it led Network Rail to cut back the tree line to give approaching cars better visibility of the track, the result being that the average car speed afterwards was higher (as they could see further).
So in making things safer, we are not necessarily always making them better.
Getting back to the specific issue at hand, I think filling calor type bottles (that don't have the safety features of refillable bottles) poses a number of risks the 2 main risks being correctly gauging the 20% but the much bigger risk being that I suspect (cretins aside) there are still a fair number of people that don't even know about the 80% requirement (it is this latter group that concern me far more).
Just my waffly thoughts.
