"how does that mean Inworldz is failing? Wouldn't that mean OpenSim is failing as well?"
No, because Inworldz charges a monthly fee per region, opensim has no monthly tier charges. If you want 15 sims on Inworldz it'll cost you maybe $900/mo., if you want 15 sims on opensim you can run them at no monthly tier cost, the comparison is $900 v/s $0 with an optional donation in the amount of your choosing.