The way I've started thinking about it is that there is a market for securing a payment network.  In that market you have consumers (users of bitcoin) and providers (miners).  It's not clear to me that if the overwhelming majority of miners stayed on 0.8 that the 0.7 fork wouldn't have still won out in the long run because effectively what you would have had is a situation where the providers abandon a large portion of their customers (0.7 users) and start providing a service that is in much less demand.  Would everyone have upgraded to 0.8?  Maybe, but maybe not.  Maybe many people would have made the rational decision to stay on earlier versions and the small minority of miners that choose to service the 0.7 fork could have earned more Bitcoin on that fork...and maybe in the long run, the majority of miners on 0.8 would realize this situation and start to trickle back over to the 0.7 fork.  The flip side of the equation is that the users have a pretty compelling reasons to use the services of the most secure network (less risk of double spends).  So, the users very well could have made the rational decision to consume the services of the most powerful network and made the switch to 0.8.  

What happened in reality is that the majority of the mining community made the rational decision to service the largest pool of customers (0.8 as well as 0.7 and earlier users).  It was rational because the risk of servicing only the 0.8 users would have been much greater.

Because of this dynamic, I doubt there would ever be multiple forks of any consequence in permanent coexistence.  I would even go so far as to say that at this point, a successful competitor to Bitcoin would have to arise as a fork of the UTXOs in the block chain (even if the competitor didn't even use a block chain).  That competitor might even have to begin life in lock step co-existence with Bitcoin, recognizing all Bitcoin transactions for some period of time while it attempts to gain market share.