Telstra just has more bandwidth than anyone else.
for the NBN, this isn't necessarily correct...
the amount of CVC purchased for customers is the key, with everyone having the opportunity (but maybe not the $$$) to buy the appropriate amount for their customers...
also, how that CVC ratio is managed is also an important factor...
telstra may have the $$$ to buy more CVC than others, but don't always do it, whereas an RSP like aussie broadband make it a part of their standard operating policy to have a % buffer on every link they have... and this can be viewed by the publicly available CVC graphs, which most other RSP's don't make available...