Unless the process of verifying compatibility is time consuming and consequently expensive? In that scenario, focusing on the more important titles would be sensible. There are over 1000 titles that fall into the ultra low budget shovelware bracket when you consider the difference between titles shipped for Europe against those in America. That is before we consider how many of those conventional ~1,500 titles are in themselves shitty. Harrison, in the intervew, implied that they are focusing on big titles:
http://threespeech.com/blog/?p=301
It's likely that of the 1000 titles compatible for launch, the majority of them will be titles also released in the US and Japan.