Nnnnnnnnnnnnnnnnnnnnope, that's not what the engagement ring was intended for.
The original point of the engagement ring was virginity insurance, and nothing to do with being treated like a princess. (The having a day to be treated like a princess is a relatively recent development, fostered into hyperdrive by this generation's current streak of narcissism.)
This is actually the original point of the engagement ring:
--"We've been courting for what seems like ages! When can we have sex?"
--"When you marry me, of course."
--"Ummm...If I promise to marry you, can we finally have sex?"
--"No. How will I know you won't just take my virginity and toss me aside?"
--"Uhhhh...why don't I give you an outrageously expensive token to wear? It will symbolize our betrothment, and if I don't follow through and marry you, you get to keep it as payment for your virginity."
--"Deal."
I wish I was joking. I am not.
Still make you feel like a princess for a day now that you know how the tradition started? ^_^