You can move some parts of some apps to the SD card - it depends on the app, not the phone. Many apps won't run or won't run properly if they run from the card (widgets - which are apps, or parts of apps - won't run), so a good developer turns off the ability to move that app. A bad developer (someone who thinks he's a developer but is really just someone who can modify a template) don't know to test his app when moved to the card, so he doesn't turn off the ability to move it, and you find out that it doesn't work when you move it.
Of those apps that can run from the card, only parts of them get moved (some parts can't run from the card), so you probably won't save more than enough space to install more than one or two more apps. That's one reason carriers allow us to upgrade our phones every less than 2 years (depending on the carrier) - not only because they want to sell you a new phone (they do), but because apps keep getting bigger, so we keep needing more internal storage space. (The reason Google doesn't write Android to automatically mount an SD card as main storage is, among other things, the fact that you could use the same phone for 5 or 6 years with no problems, and the carriers wouldn't like that. Some custom ROMs have done that, though, so the default app location is the external card.)