From kuerig’s perspective it’s a better decision to build a machine that cannot be modified, as they may be at blame and will have to spend millions on lawyer fees proving McDonald’s modified and misused their product.
- The injury due to the coffee burn was due entirely to the elevated temperature.
- The machine would not have served at the scalding temperature had McDonald's not made the modification.
- The modification was specifically made to raise the temperature to a level that turned out to be unsafe.
The question of whether a modification was made would almost certainly come out in court because a McDonald's employee would be unlikely to perjure themselves over it.
Therefore, all the liability would be on McDonald's.
Though I do see your point about legal costs being incurred even if the case of Kuering being completely innocent. It seems that having a culture instilled with a nebulous concept of "liability" encourages people to limit other's ability to take their own risks.
(Edit: formatting)
There doesn’t need to be “walk don’t run” signs everywhere, and liability waivers for every activity.