I would imagine the people that need more than 1TB would be professional photographers who use flickr as a portfolio / advertising.
If you are such a heaver user that you need more than 1TB of space, you are unlikely to want to split your account into two and your would probably be unlikely to balk at spending $500 per year on what would be for you a business service.
If you are such a heaver user that you need more than 1TB of space, you are unlikely to want to split your account into two and your would probably be unlikely to balk at spending $500 per year on what would be for you a business service.