I have to agree with most of the other posts. As I do a lot of traveling myself, my own assumption is that they were being kind and helpful.
Perhaps that sounds silly, but I have traveled so many times with my plushie teddy bears and sometimes had to hurry to get to meetings and when I returned after the maid service, have found my teddy bear(s) propped up very elegantly on the bed. I have always taken that as a courtesy, and not as an embarrassment.
My guess about your diapers is that they were simply being meaningful helpful as an expression that they felt appropriate. I mean, you did leave the diapers out right? So having them placed after cleaning the room and making the bed was most likely an expression of what they maid service may have felt most appropriate. How much different is that than folding the toilet paper on the roll? Seriously... I could be wrong, but in my assumption it would be the same way, they are just showing you attention to even the "littlest" (no pun intended) of details.
Hotels are in the business of making a profit, and as such, they want to caterer to those who stay there. I am sure this is accentuated with the staff. And while all hotels are certainly not created equal, the goal is to provide you with the best experience possible.
I wouldn't for even a second lose any sleep over this.
