The trigger inside the trigger is to prevent the trigger from being pulled from mere contact with something against the side of the trigger.
It's same with the XD.
Want to see pics of a guy who's glock went off while in the galco leather holster while getting into his car?
I have a cop friend who's glock discharched from the holster while he was climbing a fence chasing a bg. Hit his shoe but not his foot.
I've had two XD's discharge out of battery in my class and others I've found where the disconnector didn't work. Pull the slide back, pull the trigger and lower the slide, occasionally you will find one which releases the striker before the gun is in battery.
I do like M&Ps and Walther p99s but prefer hammer fired. Even if the disconnecter fails on a hammer fired gun the geometry of the hammer also prevents it from striking the firing pin.
Also you can hold the hammer while holstering which makes a discharge as close to impossible as can be.