The proper term for both the default HFS+ and NTFS is "case-insensitive but case-preserving"--that is, if you save "file" and "FILE" they will both appear as such, but cannot exist in the same folder. Contrast that with e2fs, where they can both exist, or FAT, where all filenames are converted to uppercase.
You may have gotten your information about HFS+ being case-sensitive due to a more recent innovation, HFSX. HFSX gives you the option to make your filesystem case-sensitive, but it's a well-known fact that doing so can cause things to break, so it's recommended against.
As for whether or not case-sensitivity is good, I would claim that bundling a file "Data" with an app, but hard-coding the name "data" for it, is broken, and case-insensitivity is simply tolerant of the brokenness. For many users, that sort of tolerance is a good thing, but it's also good to have a decent user-base that will get burned by it, as an incentive to fix it.