That's not stricty true as i have a few HK titles which will not work on anything apart from a NTSC-J console, this includes Every Party and the Chinese version of Halo 3. Some of the titles you have stated are from large companies, I believe that most Activision titles are region free regardless of where they are.
Sorry, I meant to ask why are all Hong Kong release NTSC region free. Or are they only NTSC-j compatible?
HK games are NTSC-J so they will magically work on Japanese machines with no issues, China is PAL so a number of HK / Chinese games are region free so they can be sold in both these countries but most of these are released by microsoft rather then third parties.
Most definitely not true. Resources & time. The only reason Guwange 360 hasn't gone to MS yet is they're waiting on the ratings for countries other than Japan and the US. (basically what Rabid Peanut Butter said... just didn't read it until too late) Also not true.