We know that before the Arvis Amidoh for Shabbos one says "V'Shomru..", Sholoush Regolim "Vay'daber Moushe...", Roush HaShonoh "Tik-u bashoufor...", and Youm Kippur "Ki V'youm hazeh...". Why is there not a posuk to recite because its Roush Choudesh (for example "Uv'Roushei chodsheichem...")?

Rallis

I note that apart from the exceptional case (perhaps) of Youm Kippur, on all of the occasions other than Roush Choudesh, one says kiddush. (In fact, if I think very hard, I might even be able to remember how each daytime kiddush begins .)

AKohl

That is good point! However m'ikar hadin, if one says pesukim before the daytime kiddush on Shabbos, one says "Zochour Es Youm HaShabbos" not V'shomru. It was Minhag Tzarfas (Provence) to recite V'Shomru (unless one fails to recite kiddush on Friday night).

Rallis

It would seem that you only recite pesukim if there is an inyan of Kiddush, which there is not on Rosh Chodesh.

Steven

There is a difference between the Kedusho of Shabbos and Yom Tov, and the Kedusho of Rosh Chodesh and Chol Hamoed. Only in a full Kedusho like Shabbos and Yom Tov, we have Kiddush. Only in a full Kedusho like Shabbos and Yom Tov, the Davening in Shmone Esre of Ma'ariv (and Shacharis and Mincho) is completely different, and that is when Psukim are inserted also before Shmone Esre. On Rosh Chodesh the Davening of Shmone Esre is like any other day (besides the addition of Ya'ale Veyovo), and in such a case no Psukim were added beforehand, (and the same applies to Chol Hamoed).

Michael FRBSH