I know that, it's just the PC side somehow didn't want to use Apple's "term", "firewire", so they used the IEEE term.
For a short while Apple charged a nominal fee for the use of Firewire, the technology if not the name. They dropped the fee but possibly continued to license the use of the name. So perhaps companies such as Sony which wanted to use Firewire decided to call it by its IEEE spec. That's my only theory.