Why do I think altcoins are valid?  Because the financial industry wants to hedge security, and one, single block chain does not give them that.  What if Gavin or some other guy issued an update that imploded the BTC network?  They're just supposed to accept 100% loss?  No, they're not going to do that.  There will be at least 5 big coins because a 20% potential loss is a lot better than 100%. Also, at least two coins have to exist for value of the first to transfer to the second should problems arise.