Slight whiff of FUD; not too strong though...
Sorry Zef, but no. You could have all your Salesforce.com-hosted data zipped up and delivered to your servers any time you like; the process can easily be automated. Not in the least difficult. They're your data, after all.
What you couldn't do would be reproduce all the functionality that Salesforce.com provides on another platform*; that is the value-add that they bring to the table, and why so many organisations consider them more than worth the subscription fee.
If you've built your own software stack hosted on a cloudy VM, then you're free to host that VM on any cloud-based provider's hardware (assuming image compatability) but you're still responsible for supporting the whole software stack yourself, negotiating responsibility for outages, failover handling etc between you and the service provider(s).
This may be your idea of a good time, but in many applications it's difficult to justify when you realise that there are other people who are more than capable of doing it far better for far less.
*Okay, you could. But you'd essentially be reproducing Salesforce.com's development budget for your own private use, losing their economy of scale and making all kinds of additional, unnecessary rods for your own back. Why put yourself through that?