R’ Moshe did not forbid shabbos clocks outright; he allowed them for lights but not air conditioners.
Rabbi Rosen of the Star-k explains the prohibition of Kitniyos as follows:
“Why are kitniyos forbidden for consumption on Pesach? The Mishnah Brura enumerates a number of reasons. One reason is that there is a possibility that chometz grains could be mixed amongst the kitniyos grains, creating an inadvertent yet real chometz problem when the grains are cooked together. Another reason is that if kitniyos products would be permitted, confusion within the general public could result in mistaking permitted kitniyos flour and forbidden chometz flour. Although these might not be problems of epidemic proportions, the Rema considered them to be real enough to forbid the eating of kitniyos on Pesach.”
As for Quinoa, Rabbi Rosen wrote:
It was determined that quinoa is Kosher L’Pesach. It is not related to millet, rice or the chameishis minei dagan, five types of grain products. Quinoa is a member of the “goose foot” family, which includes sugar beets and beet root. STAR-K tested quinoa to see if it would rise. The result was sirchon, as termed by Chazal, which means the quinoa decayed and did not rise. Furthermore, quinoa’s growth does not resemble kitniyos and, as cited in Igros Moshe O.C. (3:63), we do not consider additional products beyond what was originally established. However, recent investigations have found that there is a possibility that quinoa grows in proximity to certain grains and/or is processed in facilities that compromise Kosher for Passover status. Therefore, quinoa may be used only on Pesach with reliable Kosher for Passover approval.