Except that IH is really only compatible with IH. You can't use it with the wealth guidelines in the DMG. You can't use it with the Magic Item Compendium. You can't use it with Elements of Magic. You might even have difficulty using it with the Monster Manual.
Well, I wasn't addressing compatibility. I was addressing quality. Is IH great? Certainly the consensus seems to be "yes!" Does Sword and Fist have its moments of lameness? Certainly the conesus seems to be "Uh-hu."
So in that comparison, I've shown that the 3rd party stuff can absolutely kick ass, and that the WotC stuff doesn't always kick ass.
Which was kind of my point: anyone avoiding the 3rd party stuff because they think it sucks hasn't seen much 3rd party stuff (though they might've seen some stuff that sucks), because there are VERY GOOD 3rd party products that stand up to WotC products.
Notice how later in the post, I compared Oathbound with the FRCS, which is two things that are generally considered great that are certainly on par with each other. Again, proving my point: 3rd party stuff doesn't always suck.
Note: I'm not saying S&F was great. But you also can't cherry pick one of the worst WotC products to put up against a pretty good 3rd party product. Try matching up IH and Tome of Magic or Draconomicon. Leave S&F to compete with some of Mongoose's early stuff.
When someone says "3rd party stuff sucks compared to WotC stuff," I can pretty much choose ANYTHING 3rd party and compare it to ANYTHING WotC. Because the argument runs: did you buy, say, the Arms and Equipment guide? Did you enjoy it? Then why the heck aren't you buying
From Stone to Steel?
If you'll purchase and enjoy a rather sub-par WotC product, what stops you from buying the best of the 3rd party stuff? "Because it sucks" isn't a valid defense in that case.
And I would totally wager real American dollars (I know, not quite worth as much as Euros, but I'm patriotic like that.

) that the Arms and Equipment Guide did more sales than From Stone to Steel.
Which is part of why I pity those people who won't try the 3rd party stuff. Because their games are not improved as much as they could be. It's like someone who won't visit ENWorld for gaming advice because we're not owned by WotC, y'know? Wizards has no monopoly on quality gaming products, and it's really kind of a shame that some people continue to think so.