I'm not so sure they should be ridden off. As I mentioned (I really should find a reference for it) the age of the gaming populous is ageing, and that general demograph is pretty safe to say more timepoor than your average uni student or highschool student, and possible more able to speak with their wallets.
Using myself and my friends as an example, (tho I hate to use DG v HoN/LoL as said example) we chose to all buy demigod not only because it is an awesome game now, but because of all the excitement it generated when reading the whole "it's a long term thing for us" here on the forums. If a couple of mates decide they have more fun in same-genre betas and believe their free (or not, whatever it ends up being) content updates provide more longevity and enjoyment than the possible $9 perDG here, we may all end up getting said-game (again, just an example) and leaving DG behind. Not because we spat the dummy over anything, but for aforementioned reasons, and whilst that means DG still got our cash (and justly earned!) they wouldn't be getting the continual updates from us over the long term. If we feel other similar games lacking we won't buy their games at all, and will hang around for more updates, and SD/GPG get more fiscal stimulus from a bunch of us who like playing together.
The casual gamer has much, much sway over the life and longevity of games. Another example I'm loath to use but find pertinent, the WoW game style direction becoming much much more casual based over the years (the recent heroic raids as the possible exception). I know some people will play WoW and Aion and whatever else, but I think its a safe assumption a lot (the majority? who can say) will keep subscriptions rolling on one at a time for the majority of their playtime, not both. Similarly, I and my friends may keep our update-purchases to DG or similar games, but unlikely both.
As you said, the benefit of free to play you can go back to any old game at any time but that isn't necessarily going to entail buying updates as well if there's more benefit to putting time/money elsewhere for more effect. In a sense, one game will have killed the other from a out-going payments perspective. As I said (believe), the casual gamers en-force have much sway.