On nature ,it should be mandatory that CAD has to cleave the DNA for every 180bp .. But from DNA Ladder assay ,we know that we have many stacking .as DNA is not uniformly cleaved at every 180bp (nucleolous subunit).

By Nature it is must that every apoptotic cell has to undergo cleavage at 180bp.

Bcoz,  if it is not cleaved at 180bp .for example:  if apoptotic tumor  cell DNA  is cleave around 2kb to 5kb ,then the engulfing phagocyte may take up the abberant DNA that may be tumorogenic to phagocytic cell  ... 

That in turn will make phagocyte to become cancerous 

Chromosomal DNA is first broken into large fragments (50 - 300 kilobases) before they are cleaved into smaller nucleosomal fragments (approximately 200 base pairs). Extraction of the DNA fragments from apoptosis cells followed by agarose gel electrophoresis results in a distinctive DNA ladder appearance.