The 2 Providers is just an issue that comes out of have Telstra as the only telephone company for a vary long time, been gov run.
in Reality there is now lots of ISP and back bone providers but the Average Joe will no go past Telstra as that is all they have know for the greater part of there life.
As for internode, they are child company of Agile, which is a back bone provider. And if you go an ADSL2+ connection from the the only thing that they rent from Telstra/Optus is the Local loop(from memory taht is the team, it is the copper pair from eh exchange to the house.
They run their own DSLAM's and exchange equipment. to the Point that they have an online tool that lets you reconfigure the ADSL line profile, I can not link to the faq's about it but to give you an idea see here: http://www.internode.on.net/support/faq/broadband_adsl/adsl2_annex_m/#How_do_I_turn_on_Annex_M_mode_fo
Another big this is that Telstra has always Charged for upload, and so a lot of ISP also do this. Node dose not, I think optus still dose, but it's an discussing policy that is designed to strip thru ur DL limit as fast as posible.
While up load generally is tiny compared to DL, I had a mate that got hacked and only new about due to blowing his DL limit on the first day of the month due to the Hackers uploading lots of his files to there site.
I also used Nodes Priority plan when it was about, basically there was a pool of users that had there own pile to the net (as not to affect normal custoemrs) and you got an index based on how much you had DL'd in the last 7 days. The person with the high's index had the lowest Priority over the pipe to the net, the person with the lowest index had the highest Priority. This would mean if the pipe was not at heavy use and you had a high index you still got full speed, but during peek times you could be pushed back (how much I can not remember but I think too as low as 1/4 of full speed) but if you end up with a high index backing off for 36~48hr's normally dropped you back to a point where you where not notici8ng the lack of Priority.
Looking back at my Dl's for the months on that it when 30gb then 60gb then 30gb then 60gb, etc.
And that was on a 512kb connection
Want to know more about ISP in AU or looking at changing then look here:
http://www.whirlpool.net.au/
enjoy
edit: also node runs a large list of Free content via they re-stream it as that way they pay for the data once and so do not change there users if they hit there mirrors:
http://www.internode.on.net/residential/entertainment/broadband_radio/
More details here:
http://www.internode.on.net/support/faq/broadband_adsl/comparing_us/