They open full screen because the apps are designed for small 'touch' screens.
BUT, there is also a Windows 8 desktop for those who don't use 'info only' apps, have larger screens that the average tablet, and there is no rule which states that Windows 8 users have to make do with apps only.
There is enough 3rd party desktop stuff available, including a classic Start Menu or two, such that nobody ever has to visit the tiles. Skype is available as a desktop app too. I use it in place of MSN/WL Messenger. Anybody upgrading from Windows 7 will
know all about adding programs and utilities because Windows 7 was pretty much devoid of anything 'out of the box'.
Re Windows 8, for many users who only ever email or Facebook, the IE10 tile is all that they need. Signing up for Protopage, a home page can be set up with links, news, cartoons etc.
Add Libre Office, and now they can read, look at any attachment that might ever be sent to them.
The biggest problem is knowing how to work the Windows 8 Modern UI from scratch. If Blue brings back the X to shut down the apps, that is as much as many will ever need. I suspect that Blue will do this..