The Sefer Zikaron explains that Rashi doesn't mean to suggest that these are the only instances of the phrase, nor that this is the only possible way of understanding its significance. Rashi is merely pointing out that in these three cases there is a similar meaning.

Other commentaries point out that these three cases involve [historical] occurrences that were dictated by God to occur specifically by day, unlike the case of Avraham who chose to do it by day on his own.

As for the necessity to explain a deeper significance to the word, the commentaries suggest that the word 'בְּעֶצֶם' doesn't add anything to the plain meaning of the verse, and therefore requires explanation.

The Sefer Zikaron explains that Rashi doesn't mean to suggest that these are the only instances of the phrase, nor that this is the only possible way of understanding its significance. Rashi is merely pointing out that in these three cases there is a similar meaning.

Other commentaries point out that these three cases involve [historical] occurrences that were dictated by God to occur specifically by day, unlike the case of Avraham who chose to do it by day on his own.

As for the necessity to explain a deeper significance to the phrase, the commentaries suggest that the word 'בְּעֶצֶם' doesn't add anything to the plain meaning of the verse, and therefore requires explanation.