You forget that it takes up to two years to develop new Hardware. So if shortly after the iMac USB devices apperard they have been in development long before.
As such I a with the OP: USB was coming before the iMac.
We can credit (and I'm not sure the "credit" is an appropriate word) Apple for the fact that some of these USB peripherals arrived in tacky translucent plastic cases. Fortunately, Apple realized that those designs were serious "fashion malfunctions" and moved on....
