The issue is, 1.4 is riddled with buggs and not suitable for a production environment. 1.2 is stable, but they removed the download links off of the main page.
The packages for asterisk 1.2.x, libpri 1.2.x, and zap 1.2.x are available on the digium site, but only certain versions of the 1.2.x packages work together.