I trade on MtGox. There is 0 chance I will trade on an exchange that charges 3% each way. Just to enter and exit a trade, it's already a 6% hit.
I used to be a market maker on Bitfloor when it was around. Bitfloor actually paid liquidity providers for each transaction, rather than charging. That's the way to add liquidity to your exchange, especially when you're just starting.
1) What are the barriers faced by Indians (residents) that prevent them from trading on MtGox ?
Indian can do trading on mtgox and other trading sites, there's no resctriction about that, main problem is you can't deposit/withdraw fiat easily as international bank wire fees is quite high.
Currently it's like
Fiat -> Exchanger Fees -> Bitcoin -> Mtgox -> Bitcoin -> Exchanger Fees -> Fiat
and in this process sometimes people loose more money than they earn via trading due to exchanger's fees and price fluctuations.