They open source all of their clients (when not in beta). They maintain multiple open source cryptographic libraries, in multiple languages, which a lot of developers and companies go on to use. They have a yearly fundraiser for open source and digital rights groups, which they contribute a $100,000 to each year.

Just because their server code is not open source, doesn't mean they don't support open source. It's not an all or nothing situation. Binary thinking and classification is a very dangerous and naïve way to look at things.