It was definitely not just balancing rules patches for gameplay purposes - there was a clear deliberate intent to force people to buy new models. Complete with arbitrary changes to the game lore itself that accompany those updates: when I first started playing Warhammer Fantasy only the smaller lizardmen could ride the dinosaurs, and in the next edition only the larger ones (with entirely different new models) could.

By way of comparison, Games Workshop updates their Warhammer rules about twice as often as Wizards of the Coast updates Dungeons and Dragons.