1.) The "no advertising" post was concerning a post made by another member, since deleted. You are correct that the announcement/notification is not advertising.
2.) OEM software usually has additional licensing restrictions. In the case of Windows, it used to mean that you had to purchase the license with a qualifying piece of hardware, did not receive free Microsoft support, could never transfer the license to another computer once installed the first time, and could only replace the motherboard with one of the same make/model. Microsoft modified those terms to exclude those purchasing OEM licenses for their own use, something they did not originally intended for customers to do, but also permitted.