How can I prolong the life of my bottom bracket bearings? I have a bike with Campy components. I've found I need to replace the bottom bracket bearings annually, which is expensive and inconvenient. I do less than 2000km per year on it, largely through winter and spring. They are sealed bearings, but not cartridge style.

Is this unusual? How long would you expect the bearings to last? 

My bike shop says a lot of water and gunk get in the bottom bracket and just sits there, causing damage to the bearings. How does the gunk get in there? How would it get out? Should there be a drain hole somewhere?

EDIT: To clarify, I only ride on the road and sealed trails. So I'm dealing with water and silty/sand from the road/tracks only.

EDIT: The symptom that indicates the bearings need replacing is noise. I get a clicking or ticking in the bottom bracket and take it to the shop. It seems to be a noisy bike... I've also had to replace the rear freehub bearings a few times and other causes of noise. So I'm not usually sure enough to replace the bearings, but I take it to the shop and ask them to figure out where it's coming from.
Actually, IMO Hicks is right in the comments under the question. Now, had the problem been really that the BB is wearing out:



After you have been out in the wet, on returning to base (home), remove the bicycle's seatpost and turn it upside town. You will be surprised how much water runs out!

You might also want to try sealed cartage BB or external bearing BB. By the way, ordinary (not cartage) bearing are extremely inexpensive: 0.5 euro at my area.