Announcement itself is fine. The way you contrast "open" with "proprietary" is a bit jarring. It should be free versus proprietary, but if you find that undesirable, then just go with open/closed.
EDIT: Quite predictably, I got downvoted for asking people to use proper terminology and for promoting free software.
People just hate when you correct their semantics, don't take it personally. Many people also don't know the difference between free and open. Here's a popular article by RMS which explains the difference: http://www.gnu.org/philosophy/open-source-misses-the-point.e...
That ship has sailed. Today, "open source" means "free" in Stallman's terminology. Asking people to use nonstandard terminology in order to promote a particular viewpoint is not reasonable.
EDIT: Quite predictably, I got downvoted for asking people to use proper terminology and for promoting free software.