Top 3 players from each title team and method of acquisition
GS - free agent, draft, draft
CLE - free agent, draft, trade
GS - draft, draft, draft
SA - draft day trade, draft, draft
MIA x2 - free agent, draft, free agent
DAL - draft day trade, trade, trade
LA x2 - trade (after draft), trade, trade (assuming Odom over Bynum)
BOS - draft, trade, trade
SA - draft, draft, draft
MIA - draft, trade, ? (Haslem was drafted, Walker/Payton were free agents, Posey was traded)
SA - draft, draft, draft
DET - trade, trade, free agent, trade (since they had a big 4)
SA - draft, draft, draft
LA x3 - free agent, trade (after draft), free agent
SA - draft, draft, draft
CHI x3 - draft, draft day trade, free agent
HOU - draft, trade, draft (Horry - yes he was the 3rd best player on that team)
HOU - draft, trade, trade (the last 2 are Thorpe and Maxwell - man those Rocket teams were bad overall)
CHI x3 - draft, draft day trade, draft
That is probably far enough. It pretty easily shows that you can build a team using any method of player acquisition but generally most teams employ at least two methods and some like the Cavs have employed all 3. The Spurs really are the exception building pretty consistently through the draft and only the draft (or trading for a draft pick to acquire Leonard on draft night).