The hero games 6.0 rules sold enough for profit and to pay for themselves, later they came out with lite rule sets that didnt require a huge purchace.
now is hero games one of the top money makers of RPGs? hell no, but they did something differently than most game companies, they simply kept refining and improving the same set of rules for what 30 years now? There is massive content for their games, all dirt cheap, and a very strong following; they even have a MMO based on their Champions game.
They built a great game, stand by it, don’t come out with completely re-vamped rules systems every few years just to suck the profits out of their supporters wallets (except one time and that was over quickly) and have built an absolutely rabid set of "Hero Game System" fans who all agree it is the best system ever devised. (Me included)
(as a side note: my problem with hero game system is too much focus on math, and too many types of defenses to deal with. Also, generally speaking, you don’t throw together a hero games adventure… it takes a hell of a lot of design before you can run your weekly game.)
Spycraft 2.0 offers me the option to run post apoc, horror, and other games with it… I really liked those options.
Part of the reason I even looked at spycraft, is I was starting to feel the Eclipse Phase game I have been running for almost a year now, has slightly too simplistic rules, and the players have completely min/maxed the system (too easy) BUT what your saying is even if I really love the Spycraft 3rd rules I’m going to have to completely re-design everything from scrach for my sci-fi/espionage game. If I want a sci-fi game using your rules I’ll have to wait years and buy many more expensive books or just look elsewhere.
I tend not to agree with that kind of thinking… d20 did a great job at opening up new venues for its system (clearly) Hero Games does the same, Gurps and Savage Worlds the same, you start with a mostly generic system that people love then offer your supplements. People seem to really like your “mastercraft” base system, so why wouldn’t you want to follow suit and offer those campaign options to people willing to pay for them?
Also, regarding Eclipse Phase… I hear from designers (often) that they are upset the gamer public demands premium content, yet does not want to pay for it… on hearing that I always point at Eclipse Phase… one of the highest (if not the highest) selling sci-fi RPGs right now, and everything, every single rule book, adventure, and module is available as an absolutely free download from their website. In the year we’ve been playing EP my group has collectively bought about 20 $60.00+ books, and about 10 $20.00 supplements. We didn’t need to buy those books, we wanted to.
Amanda Palmer (a great musician married to Neil Gainman) reciently gave a TED talk about how she stays a top performing artist and still gets paid when she offers all of her music for free from her website… I would suggest watching that, and following the example of Transhuman Studios (IE Eclipse Phase) in how they (very successfully) approach selling their games.