I have already blogged about this topic on Bulbapedia, but that was mostly about new consoles.
So apparently, all the main series Pokémon games roughly coincide with the releases of new consoles or their redegins, within an acceptable 6 or so months of margin of error of course.
No, seriously, this has apparently been the case since Red and Green were released around the time of Game Boy Pocket. I was just trying to screw around with the release dates of the major games, I wasn't expecting to find some major Nintendo conspiracy.*
Though I really don't want to wait for 3DSi/2DS XL to get the XZ and YZ, or 3DSi XL/2DSi to get RagingRuby and SereneSapphire.
*Well, okay, it might just be because the redesigns and releases have the same two or one year period differences Pokémon games are, but still. I am going to stick by my conspiracy/original game homage idea.
Edit(05/02/2016): New direct link: https://www.dropbox.com/s/ci09u380ndfwn2b/Release%20Date%20Analysis.docx?dl=0