Most PhD students -- at least the ones I know in the states and overseas -- spend most of their time in school trapped in a lab or office. A few make time to "network" with people outside the department, but most have to be forced to socialize with a broader audience than can be found at the weekly beer hour.
The far more common pattern for a PhD student is to spend years busting his/her ass in near-isolation to accomplish research goals and graduate, only to find that it's hard to get a job without real-world contacts. So you're absolutely correct in the sense that PhD students should be networking, but it just doesn't seem to happen very much in practice.