Yes, it is true - to a certain extent.
Working from the lowest frequency end thee is a small upstream band, U0, which uses tones up to 32, then Downstream, D1, followed bu U1, D2, U2, D3. Whereas on ADSL all of the upstream is at the low frequency end. So, yes it appears to degrade faster because of the higher frequencies in use.
If you can run DSL Stats the graphs available will show what is happening.
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