I think the key phrase is:
we’ve taken a hard look at the declining desktop software market and the impact this has on being able to continue to provide new content, product enhancements and support that our users need.
It is probably true that overall the desktop market is declining, but that ignores the simple and incontrovertible fact that desktop products still provide a level of functionality that cannot be matched by online applications and/or services. Ancestry doesn't hold all the cards in respect of online data sources, and so we, as family history researchers, still need a way to collect, organise, and analyse data from a variety of different places. Furthermore, I would want complete control over the data that I wish to be available in the public domain, and actually I trust my own security over and above that of any online service, including Ancestry.
The cynical observer will simply read into this announcement that Ancestry are trying for encourage us to do more of our research online, and within Ancestry, and keep and maintain our results there. They, in return generate increased revenue and can leverage (horrible American term!) the investment we make by our research efforts. Do not be surprised if we soon see a charge if we wish not only to keep our trees on Ancestry private, but also if our trees start to grow beyond a certain size.
My message to Ancestry is that I'm certainly not going to retire my desktop systems yet, and I will continue to support competitors' desktop products as long as they provide the very significant functionality that Ancestry's online systems cannot. I think they have made a dumb decision.
