Yeah, the difficult part here being ROUTINELY successful. A Trip check is based on Strength, which usually isn't the Rogue's highest stat. You can have a high-level Rogue with 14 Str or less, while a high-level fighter will most probably have at least 24. That's +6 to your Trip checks (counting the bonus from Improved Trip) vs. +7 fo the Fighter. Sure, it's still better than Grapple, but I don't think you'll routinely trip high-level fighters with a rogue, even less if, say, you're a gnome and he's a dwarf. Wizards, on the other hand...