I read through the article, it's quite interesting. In short there's 2 major reasons they are upgrading for free.
1) They are doing very well (
Sales and financially)
2) Technical glitches that can occur, having to start over with their perfect 10/10 rating, and managing the system that lets them figure out how many people are playing and other things could get screwed up, vs just replacing the current system. Which includes getting versions confused of '
which one is the real version?'
Then of course the sorta third reason
3) They look awesome for putting up new free content and it drives more sales...
They mention they wanted to get away from Adobe Air which i think is a good thing as that thing is slow as balls to run.
All in all, a good read.