The weird thing is not that working at big-name companies is impressive, it's that it's essentially a pre-requisite for some employers. The promise of higher education is that it will prepare you to take the best jobs in the industry. It's supposed to be the primary credential. That something is becoming the critical factor in employment means that universities are losing and/or have lost their status as the baseline qualification.

Maybe it shows how little I know, but I think Valve and other companies who do this are doing themselves a disservice by basically using Google's recruiting department as a passthrough (and, as an autodidact programmer, I feel essentially the same about people who put it all on educational pedigree -- this isn't an endorsement of the baseline credential, just an acknowledgement that what constitutes it is shifting). It feels like an admission that they don't know how to hire, so they're effectively offloading that responsibility onto companies whom they believe have thorough vetting processes.