There are two parts to what we refer two as root. A rooted ROM allows you to run apps as the root user. This is what you're doing when you use titanium backup. The second part is to unlock nand. That simply means you're turning off security on some of the internal partitions so that you can write to them. You're able to make it looks like you're removing the app only because you're the root user. Since you didn't unlock nand, it didn't really remove anything. You need S-OFF before you can make changes to the system partition. Some phones come this way, others don't. The Evo comes with S-ON, so z4root is temporary. If you root using unrevoked, it will root your ROM and unlock nand. Not only will you be able to make changes to the system partition (uninstall bloatware), but you won't need z4root, as unrevoked does the same thing as part of the process.