Well, the airlines I worked for during the last about ten years didn't and in fact many had the in situ oxygen charging equipment removed per mod. The pilots can not do a visual inspection of the cylinder valve before every flight, especially if the cylinders are sited somewhere behind cargo sidewall panels or in the E/E bay. So it up to us to do a proper check upon installation.
Not all aircraft have the option to check for the valve status like on the Airbus. In most cases it boils down to do an ops check of the masks while watching the gauge for pressure drop.