Microsoft is arguably the best in the entire software industry at maintaining backwards compatibility. They go to extreme lengths to maintain support for older code and it's relied upon by many major enterprises so you're not going to run into issues unless you're planning on having something running for 50 years.
No it’s really not. We’ve been left SOL on numerous occasions and the churn rate is so high that it’s literally only safe to use the bits right at the middle of their products. And we’re talking on a relatively short three year window here.
WPF is still supported and developed. Appfabric/velocity is now Service Fabric which has much more functionality, runs many Azure and MS cloud services, and is open source.
Silverlight was unfortunate but overall good for the web. You must realize that even Flash, the vastly larger competitor, also died and gave way to much better browser native APIs.
I don’t know about Windows workflow but it’s important to keep in mind the difference between abandoned products vs the changing software trends landscape.
