Nice article, except for one line where you say
"For example, hosted applications make more efficient use of hardware than on-premise servers"
I think that's a huge generalisation and certainly not true, just because the hardware is on your premises or not.
You could argue that the efficient use of the hardware is no longer the subscribers problem, but of course it is, because if salesforce do a poor job you'll end up paying more.
The other problem is of course if the company goes tits-up or gets sucked dry by some legal argument you can't easily take your toys and play elsewhere.
Finally, they've got you by the short and curlys once you've migrated to their platform. At least with SAP you could stop paying for support while you migrate away. In fact you could stop paying full stop and fight them in the courts if they upset you enough, while you're application continues to run. With salesforce they can always pull the plug.