Home users dealing with small amounts of data can always back up their contents using cloud services like Dropbox and Box.net.[...]However, the former is not suitable for large amounts of data (say, more than a few hundred GBs),
For small amounts of data, an online backup service should suffice.
Serious businesses always have an off-site tape backup or some other similar mechanism for data backup.[...]and the latter is not suitable for making a disaster proof copy of files changed recently.
Many small and medium businesses continue to remain paranoid about cloud storage.
I see your point about Carbonite and CrashPlan, but what is the guarantee that the company won't shut shop suddenly?
Rather than trusting someone with their backups, some people might prefer to have their data close by.
I won't comment on the real time online backup offsite comment, but I do know of companies personally which do an offsite backup once a week...and I am sure they have their own reasons for choosing ioSafe as their disaster proofing solution.