So far as I know, version 4 and 5 of AC are still available, and can be used by those who just want a simple EMR.
There have been no bug fixes on versions 4 & 5 (imported items, slow eRx), plus these versions don't have updated medication list either, so you can't eRx newer meds.
You can't abandon updates on your older versions if they are offered as the "lite" version of the main product.