Historically FW was a better interconnection - more reliable, able to carry more power, better sustained data transfer speeds; but USB was cheaper to implement. FW was adopted by others (usually for camcorder connections but was also on Wintel-machines). USB2 did start the erosion of the benefits of FW.

Futures
The use of Thunderbolt - which is developed by Apple and Intel - is the promise of even faster and reliable interconnections. USB3 hasn't got going. The marketplace is not only about the consumer who is often using wireless connections (WiFi, BT, etc.) but also enterprise (who are moving more to VDI, etc.) but there are also the specialists who want interconnections that are fast, reliable, easy to connect. The future is large data - whether video (moving to higher and higher definition); audio (think of recording with higher definition audio with lots of tracks); even things that we did not imagine (off-loading specialist data transformations such as an encoding devices) as well as the usual storage needs that grow and grow - not everything can be put into the cloud - even with a good internet connection - editing video, audio, graphics is just too much data to move over a network connection. This is the main future for ThunderBolt and even USB3 for a while.