1 - some games (not all, to be sure - few is probably the right word here) are made free after quite a bit of time goes by - as in years and years. With Demigod available indefinitely digitally, I doubt that day will come as there will always be potential to make some money from a sale down the road. Not exactly a solid business decision to give your product away for free with no expected benefit.
2 - If you are talking about a free to play model, like league of legends, etc, well, that would require significant changes to the network code, a permanent Demigod staff to create new characters, etc, etc, etc. We are talking about a colossal investment. Personally, I don't see that sort of thing happening.
Anyway, its a fun game and always good to see it showing up on more and more digital platforms as that has potential of reaching more customers that are dedicated to a specific digital distribution platform.
Also... necro ftw...