All of the people that bought Windows Phone 7 devices (even if it was last month) won't be able to run any of the apps complied for Windows Phone 8 because it's core is based on Windows 8.
How do you expect your dedicated user-base that for years has been complaining about slow hardware and a lack of apps while the iPhone, GS3, etc has been blowing up to react? All of the current Windows Phone users are not going to buy a new phone to make their current phone, that they purchased six months ago work. They're going to pickup and iPhone 5 or a Galaxy Note. They have a core base of users that are passionate about Windows Phone, many of those I know are leaving.
Having spoke to startups that have apps on Windows Phone, most of them have been paid by Microsoft to hire a developer to build it and aren't going to be updating it. Unless Windows Phone got a huge lift in traction but the chicken and egg problem is stopping them and all of these old apps have to be rebuilt for Windows Phone 8.