I don't think "number of registrations received when offering only Facebook Connect" is enough data to evaluate the effectiveness of using Facebook Connect as your only login option compared to providing a real login option.
Edit: It looks like your product actually depends explicitly on Facebook data to work, so it wouldn't be possible to not use Facebook. While Facebook Connect is a good choice for a product like that, it is also the only choice.
I agree with you, I'm not trying to make a general statement that is true for everyone. Just trying to point out that FB Connect might not be viewed as negatively in certain markets.
Edit: It looks like your product actually depends explicitly on Facebook data to work, so it wouldn't be possible to not use Facebook. While Facebook Connect is a good choice for a product like that, it is also the only choice.