Except that companies like Microsoft and Google register domains through "Enterprise" registrars like MarkMonitor, who charge upwards of a few hundred (possibly even thousand) dollars per year for their service - which supposedly includes "not letting the fucking things expire" and "making sure other people don't register our damn marks".
Microsoft actually has even less excuse in this instance, believe it or not - Microsoft's certificate vendor is itself. All MS certificates are chained up to a Microsoft subordinate CA (with a GTE root). So it wasn't a failure to pay for a certificate since they don't actually pay for them - it was just someone not bothering to open the certificates MMC and click "Renew Certificate". Hell, it's probably even AD integrated so there's no need to fill in any fields.