The problem is that JARs are the Joint Aviation Requirements, not Regulations. Member states can only implement those requirements within the framework of their individual national law. Most member states, UK included, cannot implement certain elements of JARs because their national law prohibits it.
This will be solved, in the case of those JAA member states that are also members of the EU, when EASA takes over licensing issues (currently due in 2006-2007). JARs will then be enshrined in EU law, which takes precedence over national law, and all EU countries will be legally obliged to comply with all parts of the requirements (goodbye US training?). The downside is that the UK CAA will probably lose the flexibility it currently enjoys in implementing the requirements and wannabees will have to deal with faceless bureaucrats in Cologne instead of Gatwick.
However, EASA will only function in EU member states, a number of JAA states are not members of the EU and this is set to increase as many Middle East and South American countries are looking to join. In solving one problem, it is likely that many more will be created.