The Joomla templates you see are not "one month knockoffs', a considerable amount of time goes into the planning a progression of the themes the teams release.
The theme you see in August was not started on July 1st with a July 31st deadline.
E.g., updating the fusion menu based on customer request started a few months ago, and it's taken the team a bit of time to come up with the megamenu, that's now available.
Basically the process is linear, not simultaneous, as a simultaneous development would not be feasible.
The team and moderators pretty much work up to the last minute for the monthly release as there are so many final tweaks and fixes required to release a stable, professional design.
Once the Joomla version is stable, the team members have a solid design to work with porting the theme to other platforms.
Since the inception of the phpBB3 club, the phpBB3 themes have always been released one month after (give or take) the Joomla templates as it takes quite a bit of effort to port the design and functionality from Joomla to phpBB3.
Now we offer WP and Drupal themes, but as I mentioned before, it's not an instant process of converting a theme from one platform to another.
It takes time, and the team is dedicated to the philosophy 'we will not release a theme until it's ready for a production site', i.e., something could be released before it's ready, but it would only cause you (and RT) lots of trouble if it doesn't work correctly.
All in all, expect themes current themes to be released in other platforms to be release about a month after the Joomla release. (Sometimes it takes longer, e.g., converting WP along with adding Gantry)
As far as porting all the old themes, again, it's a matter of priorities, (the most popular themes are ported first) i.e., does the team focus on creating a megamenu for other platforms and release it with the most current themes or port templates that are several month or a few years old?