Yes, there certainly are alot of traded rucks.
But there is a difference between just rucks and premiership ruckmen.
Let's have a look at the premiership ruckmen to see who was traded.
2005 - Sydney - Ball & Jolly - yes
2004 - Port Ade - Lade & Brogan - no
2001/2/3 - Brisbane - Keating, Charman & McDonald - no
2000 - Essendon - Barnes - yes, Alessio - no
1996/0 - McKernan & Capuano - no
1997/8 - Rehn - no
1987/95 - J.Madden - yes
1992/4 - Irving & Ball - no, Harding - yes
1993 - Alessio & Somerville - no
1986/88/89/91 - Dear & Dear - no
1990 - Manson - no
1984/5 - S.Madden - no
1983 - Byrne -yes, Paton - no
1979/81/82 - W.Jones - yes, Fitzpatrick - no, P.Jones - no
1980 - Lee - no
1976/8 - Walter, Scott, Jones & Paton - no
1977 - Keenan - yes
1975 - Nolan - no
1973/4 - Roberts, Green & Balme - no
1972 - P.Jones - no
1971 - Scott - no
So 25 years of ruckmen.
Certainly a mixture.
The gist I get is that nearly all the truly great ruckmen who made a long term contributions to their club came from that club. Justin Madden was the only exception, but he was traded as a boy.
The traded ruckman only stayed 2, mabe 3, years at their premiership club, to fill a hole.
From this, my feeling is that we should be nurturing 2 or 3 junior ruckmen, with the hope that possibly 2 of them come on.
When the Tiges are a real chance for a premiership, but may have a hole in the ruck, that's the time to trade.
Of course, with the J.Madden precedent, you can trade to get a junior ruckman.