I can confirm that there are features of Android which are not documented. I was looking for a way to access the screen of the VPN-settings programatically and I finally found the way by using an intent but it was not documented in the SDK-documentation. I later found out that it was not documented due to restrictions in China which Google decided to adhere to.
What regards reading incoming SMS-messages, it could be a similar issue but in this case due to privacy-concerns. I wouldn't like a program/service running in the background that without my knowledge is perhaps spying or forwarding my incoming SMS to someone else using the internet-connection of my Android.
Just some thoughts....