Regardless of whether there is a Professional commercial product - Is the Community Edition (free version) improving?
I would argue it is - 5.1 has enhancements over 5.0 which had enhacncements over 4.9, and 5.2 will have enhancements over 5.1, and with the resources at our disposal the speed of improvements is increasing. We currently have a team of 6 developers (where we used to have 3 - 2 of whom Joe and Shaun were focussed on other things for a large portion of their time).
It is true that 5.1 Professional has more features than 5.1 Community, but there is no intention to cripple the Community Edition, and most of the enhanced features of Professional Edition depend on enhancements to the core, which benefit both products.
It is also true that at some time in the future the investors will need to recoup their investments, but the success of a commerical DotNetNuke product depends on the success of the Community. Without the Community - the ecosytem- there would be no Professional edition, no Marketplace, no Open Force conferences and no company.
The comparisons with Community Server are not valid. Community Server was never an Open Source product - Teligent provided a free version of its commercially licensed product fo those with limited requirements. There is no community around Community Server.