@gf,
we are talking about Japan here aren't we...? As mentioned before, purchasing a platform doesn't mean that the country has to abandon everything else. At the end of the day it's up to the country in question to elaborate on whether a new platform fits the existing and/or possibly planned system or not. I just don't see why a Typhoon shouldn't fit the JASDF's force structure, it's not like they are going to buy a Russian plane which would be entirely incompatible on all fronts. There would be no need for the UK or the rest of the partner nations for that matter to supply Japan with a whole warfighting system. The Japanese need to integrate the platform of choice into their existing structure.
Yes, the discussion is about Japan, what GF was attempting to point out is that in discussing the merits for Platform A vs. Platform B for various roles, it (still) is not just about which particular platform is cheaper/faster/longer-ranged/whichever particular platform metric people attempt to compare...
Systems constructs involve more than just whether or not a particular sensor, comm system, or weapon is NATO compliant or not. Part of the systems construct is going to involve methodologies, operating practices, and non-standardized systems. Take helicopters for instance. Most helicopters have tail rotors for flight stabilization, to keep the helicopter from essentially spinning around. US and Euro 'copters have their respective tail rotors (generally) designed to spin in opposite directions from one another, and this is a result of design and (helicopter) system elements like the turboshaft and engine. While not necessarily a major issue, if Japan where to consider purchasing a new military helicopter, some consideration would need to be given before Japan would proceed to purchase a 'left' spinning helicopter if the current helicopter fleet were all 'right' spinning, or vice versa.
With that above, whatever Japan (or any other country looking to purchase kit) chooses to purchase, needs to be able to fit into the current and projected future system constructs, during the service life of the piece of equipment. While being NATO compliant is a start, there is more to system construct integration than just that. Given the extensive amount of R&D the US does, as well as the formidable logistical footprint the US maintains, those both could give a US-based product an advantage in a competition, especially with a country like Japan which already utilizes a significant amount of US kit, or US-based kit designs.
-Cheers