If I'm reading the question right I think Mike had it.
A gun firing in SA - whether it's SAO or DA/SA - is going to have a very short pull where as a gun firing in DA is going to have a longer pull. 1911 trigger's for instance have an almost unnoticeable amount of travel.
It's going to be harder to unintentionally apply the hypothetical 5.5lbs to a DA trigger for it's entire length of pull than it is to bump a SA trigger with the 5.5lbs.
Guns with relatively short and light DA (or whatever they are) triggers (glocks and the like) mitigate the risk by having passive safeties that make it harder for the trigger to be pulled unintentionally, or in some cases (like the M&P line) they give you the option to have a mechanical safety as well.
si vis pacem para bellum