I would assume that the primary difference between 10base-t vs 100base-t is the speed of the clocks interpreting the electrical signal. In other words, if you ensure that a "bit" is transmitted in 1 micro-second, you could fit 10Mb of data down the wire in a second. If you ensured that a bit is transmitted in 1 nano-second, you could fit 100Mb in a second.
If that's the only difference, then every "100base-t" cable should be able to support transmitting data at 10Mbps as well.
Is this true? Or is my initial assumption wrong and there's more that's physically different between those two protocols?