I hope not, simply because I honestly believe that a public proposal is one of the worst things someone can do to a person that they love.
Case in point:
http://www.youtube.com/watch?v=UtPkxzHKLpk
Most people feel essentially pressured into saying yes, even if they want to say no. (Trust me, I know someone who did this. The girl said "yes", but didn't want to. Very messy eventual breakup.) And if they do say no, they are forced to experience the worst humiliation in their life. (See attached YouTube link - that poor girl. Jebus.)
The only way the public proposal can go right is if the proposee absolutely 100% has no doubt in their mind that they want to marry the proposer. Even still, the proposer may always have doubts and wonder if the proposee only did say yes because it was public.
Besides, it is an important and highly personal moment, so there is nothing wrong with it being privately shared.
This is just my opinion, but I believe it very strongly.