There are lots of 10G cards that also do 1G, but I don't think you'll find
any device drivers for 1G-only cards that work with the quite different
hardware that does 10G :))
Fundamentally though most of the hardware (as in the physical components
on the 10G board) that does 10G is also used to do 1G; and most of the
hardware that does 1G is also used to do 100M. The protocols could be
considered distinct, but they're so similar at heart that giving them the
same name seems sensible to me.