"As far as the hotel is concerned, you're the only person who can see (your bill). But they're sending your confidential data over the air through a broadcast system. It's the equivalent of running an open wireless access point. If I tune my TV to your channel, then I get to see what you're doing,"
The interview with Wired magazine goes into some details on how a clever person can get services for free and even tamper will your bill. The subject of the interview apparently discovered this flaw when he was, quote, "mucking about with hotel TVs to get the porn channel without paying for it." Nice.