Actually, most people have only 5 pages -- but you (and Lance) can see deleted rooms.
So, as you see, rooms do in fact get auto-deleted. From the FAQ:
Rooms will exist indefinitely, so long as there is at least one person actively talking in the room. A room is considered worth retaining if it has more than 15 messages by at least 2 users. Rooms not worth retaining which are inactive for 7 days will be deleted. Rooms worth retaining which are inactive for 14 days will be frozen. Frozen rooms do not allow any new messages to be sent, and are not shown in the default room list to prevent cluttering the rooms interface.
The last part is still to be done -- currently all frozen and (for 10ks) deleted rooms still clutter up the list. Although in the standard view (i.e. sorted by activity), they'll be sorted at the bottom. Removing the frozen and deleted rooms from the regular index will leave about two pages, which isn't too bad.
We're just not sure about the exact implementation of that, but I'm pretty sure we'll have a decision on that within about… meh, that joke is getting old. You know the drill ;)
Update: I just noticed I hadn't followed up on this; this has been implemented for a while now. Frozen and deleted rooms are hidden from the normal rooms list and will only be displayed on request.