Indeed. To make your point more explicit: My girlfriend has my old iPhone 3G. Given that iCloud will not be supported on the 3G, she will have to buy a new phone once the MobileMe subscription runs out, to continue to use the handy synchronization features of MobileMe.

Now, it's just calendars and contacts, but as documents, "App state", etc. moves into iCloud, people will feel necessary to update to the latest device more often to be able to use iCloud in its fullest.

Every year you do not upgrade your device, you will miss out on more and more improvements, until your device becomes unsupported (the iPhone 3G was obsoleted well within 2.5 years).

iCloud and comparable offerings will make digital life easier for many people. But it will also be a lot harder to get out of the vendor grip. People will dislike these companies as much as they disliked Microsoft, but will be equally tied to their products.