I'm not sure about too thin (although I switched to the qi-charging back after a year), the replacements /where/ thinner.. but lost the IR blaster, replaceable battery, eventually μSD housing, eventually headphone jack.
I did ruin the water protection on mine pretty quickly though, because the back panel was made of plastic and was... flimsy. It basically became a fidget toy.
When thinking of how flagship phone producers are going to keep making sexy phones that also keep their watertightness, my biggest worry is repeated stress from any removable component becoming a fidget toy