I suspect that the definition of "maliciously interfere" is the tricky part to define. In this case, the convention center was effectively DOS-ing its visitors/customers to vendor-lock internet access, which is as clean a case that a court could receive.
AFAIK (and IANAL) in the USA (IANAL in other countries either :)), some areas even criminalize the act of intentionally joining an open wifi, so I imagine a court could be extremely broad in its definition of "interfere" -- in our technophobic atmosphere, I wouldn't be shocked if this extended to scanning for SSIDs outside of the context of the OS.
