I originally thought you actually needed to be situated in the Indian Ocean in order to get a .io domain. It might lead to some confusion (although I assume the tech savvy generally look at the TLD).
That is no extra restrictions. They do have this in their terms (most notably, for any purpose against the laws of any nation):
No .IO domain may be used, directly or indirectly, for any purpose that is sexual or pornographic or that is against the statutory laws of any Nation. In the event of NIC.IO being advised by any party that a specific site breaches this condition then NIC.IO reserves the right to immediately deactivate the offending registration. The applicant may seek the reinstatement of any suspended domain name by seeking a determination by an Arbitrator appointed by the World Intellectual Property organisation.