It doesn't necessarily indicate that there's any problem, your ISP may just not send a response when the TTL expires. Traceroute essentially works by incrementing the TTL ("Time To Live") value by 1 on each packet it sends out to the network, then it waits for a network device to respond saying that the TTL has expired and records the address of the network device that responded and the time it took to respond; that's the output you see when you run the command. A network device can be configured so that it doesn't send the TTL expired notification, and after a certain amount of time the traceroute program just gives up on that packet and records the "*" value, which simply means it didn't get a response to that packet. So, that could be because there's a problem between you and that particular hop, or it could simply mean that they're not responding. My ISP is Comcast and they don't respond from the first hop into their network, but they do respond for all subsequent hops within the network; I'm not sure why, it's just how they do it. When you traceroute out, do you get replies from hops beyond the first one, or do they all time out? Again, the traceroute results can be useful if you understand the implication of the results, but they don't necessarily mean there's a problem.
Edit: Sorry, all that and I neglected to answer your most direct question -- your cable modem isn't a hop, so if the lack of a response was indicating a problem it would be between you and your ISPs first network device.