I'd say the term "ideal" means suited to your riding needs and comfortable to your body.
Thus, a beginner rider who is not athletic does short flat neighborhood rides might indeed find a frame that puts her in a more upright position, and with straight bars for instance, and few gears, to be "ideal". Later on when that same rider is in better shape and wants to race or do long distance touring she would find a very different frame to be "ideal" then. People change, their bodies change, and their biking needs change.