Table top's major investment is figurine(s). The old truth is that you can always rewrite rules as long as figurine scale remains same and previously bought figurines remain supported by new rules.
This is only true if the revenue generating component of the company's game line is in mini and mini-related sales. This does not apply to companies not based on this model.
GW followed/follows this model pretty closely. The historic bulk of their revenue generation has been through the sales of Games Workshop miniatures and miniature-related products, like Citadel paints. Game supplements were historically light; Army books for the most part. Game supplements were designed to support a heavy emphasis on the artistic sides of the "hobby" (with hobby defined as the collection, painting, modeling, modification, and playing of GW miniatures).
In 2006-07, with the recession starting to creep GW began publishing additional game supplements to expand game mechanics and universe. The expected outcome was to strengthen the gaming community with play variety and nation-wide campaigns. While the supplements were a back drop to the continued rebranding of GW's miniature lines, they were never a focus.
This is extremely important.
From a sales perspective the supplements were never hot sellers – that wasn't the point. Instead, they provided the relatively static universe and game with new material – effectively a booster shot while the economy slowed down and the miniature rebrand continued.
One of the biggest coups for GW was the Armageddon Game Rules. This effectively codified serious Big Game play into something any GW player group (or retail store) could manage. Coupled with new models and tournament support, and there was a major upswing in bread and butter sales (i.e., miniatures and miniature-related product).
You wouldn't believe how many new and old players dished out cash for a Baneblade once those rules were published. It's one of the major reasons why GW converted the model over to plastic almost immediately – Accessibility was worth the capital outlay to meet the demand.
Again, in this example game supplements supported the major revenue generating products, with a focus on strengthening the long term investment of the customer.