No ISP is going to change the present pricing of adsl. sorry that should read Telco instead of ISP. why would you if you can get enough cust paying the nice high price that telcos are currently charging. if this were not the case then telstra cable connections would be half the price with no data limits. But instead they are priced at the same (if not more) than ADSL connections of the same speed - 4Mb (3.5Mb).
Telstra do not offer the good old cut to 64k if over the limit, they would rather charge you more money. this would be fine if you had a choice - i want to go over my limit and pay vs cut me down once i go over so i know what the bill will be each month.
just my thoughts on the present price structure.