I completely agree with you here. 

It’s clear that William has some seriously issues in regards to his mother. I mean take the engagement interview when the interviewer asked about the ring William said 

 It’s my mother’s engagement ring so I thought it was quite nice because obviously she’s not going to be around to share any of the fun and excitement of it all - this was my way of keeping her close to it all.

So basically he’s saying that Kate is carrying round the memory of your mother, but at the same time you don’t want people to compare her to your mother. That’s logical thinking.

But you know, that on it’s own wouldn’t be so bad. But the wedding took place in Westminster Abby the same place his mother funeral took place AND the music (  Guide me, O Thou Great Redeemer) Kate entered the Abby was the same music used as Diana’s coffin was carried out of the Abby and Kate is wearing Diana’s ring.

* Shudders!*  talk about creepy.

William still has not gotten over his mother death and like you said has not grown up. I think mainly due to the Middletons and palace staff indulging his every whim.