It is Coming
Using Australia as the example. The majority of their systems have existed for a while and do batch processing for the majority of the transactions, most of the time running overnight. As the newer systems are coming into place (internet banking etc) it is starting to become instant. The issue being that many of the legacy systems simply were not built to do real time processing.
In saying the above though some Australian banks are in planning to move into what they call their "Real Time" systems, involving major rewrites of critical software. Commonwealth bank for example is mid way through completing these tasks, with parts of the system completed in use, and are the first here to undertake it (see http://www.commbank.com.au/personal/accounts/real-time/ ). Their child bank, BankWest is currently planning to update their systems to complete this based on Commonwealth Banks success.
National Australia bank are also currently in the late design / early development phases of their "real time" project called "NextGen", as well as multiple other core upgrades. See http://delimiter.com.au/2011/05/06/this-is-the-year-for-nab-core-banking-overhaul/ .
So yes it is coming, but it takes a long time to update such large and critical systems (especially when they still technically work and cost upwards of hundreds of thousands of dollars to upgrade them)