http://store.steampowered.com/subscriber_agreement/2. LICENSES
A. License Terms.
You understand that for reasons that include, without limitation, system security, stability, and multiplayer interoperability, Steam may need to automatically update, pre-load, create new versions of or otherwise enhance the Software and accordingly, the system requirements to use the Software may change over time.
You understand that this Agreement (including applicable Subscription Terms) do not entitle you to future updates, new versions or other enhancements of the Software associated with a particular Subscription, although Valve may choose to provide such updates, etc. in its sole discretion.3. BILLING, PAYMENT AND OTHER SUBSCRIPTIONS
ALL CHARGES INCURRED ON STEAM, AND ALL PURCHASES MADE WITH THE STEAM WALLET, ARE PAYABLE IN ADVANCE AND ARE NOT REFUNDABLE IN WHOLE OR IN PART, REGARDLESS OF THE PAYMENT METHOD, EXCEPT AS EXPRESSLY SET FORTH IN THIS AGREEMENT.