It is no surprise that open source technologies find widespread favor in governments. This is true for both server-side and client-side operations. In fact, many widely used web technologies were created and fine-tuned in government organizations.
Governments have unique requirements from their software solutions. Unlike private enterprises, there is no short-term liquidity event on the horizon for government agencies. Governments have to make judicious, long-term tech choices, which is why open source curries such favor in the public sector.