No this is not a scam. The difference, ripple is controlled by a company just like paypal, payza, moneybookers, libertyreserve, webmoney, perfectmoney. They are created for profit.
It is at the moment, but it is stated that it's in beta. People who believe in it count on the fact that it will become open source and distributed.
Ripple is no more than a promise.
Do you use an exchange? The numbers you see in you balance are a 'promise'.
Just don't trust people you wouldn't trust otherwise.