Originally Posted by
watercooled
When you say exposed, do you mean responding as closed rather than 'stealth'? Either way, it's not necessarily a problem in itself, as long as they're not forwarded, it's no more a security risk than responding to ICMP for example. If the Homehub itself is using them for something it may be a different story. However, it may simply be that BT is blocking the ports on its network, responding as 'closed' before they even reach your router; lots of ISPs do this on vulnerable ports like SMB/SSH/Telnet/etc, just some drop packets while others reject.
About XBMC, are you talking about a LAN-LAN connection? Unless it's through a wireless connection, the LAN side is simply a switch so should have no impact.