Richard Harrold at My Buddha is Pink recalls an explanation from a monk of why Buddhists bow. I like it.
He explained that the bowing down before a Buddha statue was not an act of obeisance as if the Buddha was a deity, but rather an act of respect. He used the example of a parent’s or grandparent’s grave. If you had respect for them while they were alive, you often continue to show that respect by assuring that their grave is kept nice. On special days you may put flowers on the grave. If the headstone becomes dirty, you clean it. And you spend silent moments occasionally in reverie at the grave, remembering what your parents or grandparents taught you. If you do not live near the grave, then perhaps there is a special photograph of them you keep, or a photo album. That is what we do, he said, when we pay respect to the Buddha image or a Buddha shrine; we are showing our gratitude for the Buddha leaving for us the Dhamma. When we chant, we are not praying because there is nothing out there to hear our prayers. We chant because it reminds us of the Dhamma and focuses our minds.
This explanation certainly appears useful for putting bowing in a perspective that is easy for non-bowers to understand.