You are certainly correct in your observations of the "lurker" crowd. No matter the site mechanics, there will always be a large component of site users that browse content aggregators for, well, content, rather than the community.
However, for those who are a part of the larger reddit community and (as amusing as it is to say this) actually care about karma points, Hubski offers an alluring system to quantify social acceptance. Users only need 8 dots to earn a badge, and with no possibility of being "downdotted", earning badges seems to be an easier goal to accomplish than racking up thousands of karma points.
Hubski offers a crisp, customizable content feed that people who like reddit will find familiar. With the comparative easiness of racking up badges, Hubski will likely attract lurkers and avid users from reddit alike.