:O really? not for medicine though- I've heard the UK govt sets a certain quota for amount of medics to be admitted each year.
OP- from what i've heard, for some subjects it is definitely better to go to Cambridge for the interview, though officially, it shouldn't make a difference.
When interviewed overseas, the interviewer is not necessarily from the college you applied to. They are part of the international team. When you have your interview, they write up their comments and recommendations, which then gets sent off to the college you applied. The college will then review it along with other candidates interviewed in the UK.
However, bear in mind that getting interviewed overseas means that you'll only have one 30 minute interview, not two or three you will get going to the UK. Having more interviews mean that it's less risky.
I was originally going to have it in Malaysia but it clashed with an exam so I ended up going to the UK instead. I was happy about how things ended up...my college looked so pretty!