Part of the new Dev Centre is support for in-app purchases, but this will only be available for apps targeting Windows Phone 8.
Ubergizmo speculates that this means Windows phone 7.8 will also lack the new Wallet app, which is tied into paying for purchases on the new platform.
A bigger and more important implication however is that it will speed the movement of developers to Windows phone 8, even when the legacy Windows phone 7.x population is much larger.
In-app purchasing on iOS and Android generates much more revenue for developers than the purchase of the apps originally, and allows developers to compete with free, ad-supported apps.
If developers can earn more from their Windows Phone 8 apps even with a smaller number of users (say 10 million WP8 vs 20 million WP7.x by Q2 2013) it is likely that support for the legacy OS will drop off much more steeply than previously anticipated.
At this point it is unlikely anything will change, but the wedge which is separating Windows Phone 7.x and Windows phone 8 has just been driven in a bit deeper.