I am not sure what you mean by "Quan Pu comparison," and so maybe what I write may not be useful.
First, in the form list I have, Cheng Man-ch'ing's form has Step Forward, Plant Punch, but not Punch to the Groin. even though the illustration might suggest otherwise. The English name given is "Step Forward and Strike with Fist," but the Chinese is shown as "Chin-pu Tsai Ch'ui," which refers to the "Planting Punch" or "Punch Downward." In Pinyin, the Chinese would be "Jin bu zai chui."
As for why these postures were deleted, I have read that an important goal of Cheng Man-ch'ing's was to reduce the length of the form to the "minimum." In the book I have, 3-5 minutes is given as the time necessary to do the form. Given that idea, I can speculate that the thought process went something like:
1. Keep the traditional form sequence, but eliminate as many repeats as possible that will not force a change in the sequence or change the desired flavor. (E.g., keep only one repeat of Cloud Hands, while permitting multiple repeats of Grasp Sparrow's Tail.)
2. If the form is still longer than desired, eliminate similar postures that are almost repeats (e.g., White Snake Spits out Tongue, Punch to the Groin, Cross Shaped Legs) and the associated sequences.
3. Eliminate postures that require lengthy transitions that incluce repetitions. (E.g., Strike Tiger and Twin Peaks to the Ears, which are preceded and followed by kick repeats.)
4. If the form is still too long, modify the sequence in such a way that you can delete more linking movements whose flavor is not as much to your liking or that you consider less necessary. (E.g., the change in sequence after Flying Diagonal that includes Cloud Hands, Squatting Single Whip, and Golden Rooster and that allows deletion of repetitions of Lifing Hands, Brush Knee, Defect Downward-Parry-Punch, Grasp Sparrow's Tail and Single Whip, and that also requires complete deletion of Needle at Sea Bottom, Fan through the Back, Turn Body and Chop with Fist.