Except when you make 75% of your revenue off of slow moving IT departments who use complex VPNs and Firewalls.
When they do, they better move to your cheaper alternative.
When they don't move at all, there always is the rest of the market that might move there. For example, if you buy cloud box, your Internet provider could give you 'free' Office in the cloud, just like they give you 'free' antivirus now.
I do not think this is an outrageous prediction. Both Google (Chrome OS) and MS (Office Live) are already moving there. One could even (weakly) argue that iPads and iPhones just cache cloud-based executables; Apple 'only' needs to fix its data storage solution. My bet is that that is what their rumoured new data center is for.