Whenever I upgrade Delphi I have never purchased the "1 year Update Subscription". I don't understand what some of the provisions really mean.

Whenever I upgrade Delphi I have never purchased the "1 year Update Subscription".  I don't understand what some of the provisions really mean.

For example what does each of the following really mean:

* Updates and hotfixes for the current major release
* Ongoing Maintenance - Updates and hotfixes for up to 2 years and 3 major releases
* All major upgrades ( ie XE7 to next major release )
* Annually renewable at a fraction of a single upgrade cost