My knee jerk reaction is to agree with this post— it's design by committee, shed painting, whatever you want to call it.

"This just makes me think that each individual app team submitter their own design for an icon based on some loose guidelines and they all got thrown together into a bucket"

Probably resonates with me the hardest— personally, I think the apps look great, but the icons really just look "off" to me. To each their own, I suppose.