Religion is not an expression to be only defined by definitions invented by Christians or by modren civil rationalties.Bigfella: You've gone to some lengths to make it clear to me that many/most/all Indians don't accept that non-indians can be hindu. This indicates to me that an element of race/ethnicity has strongly attached itself to hinduism.
Spread of Hinduism can not be compared with spread of Islam or Christianity. We know it because there is no authority to governs who is coming in and who is going out; no body cares.
Element of race or ethnicity should work both ways i.e. coming in or going out. A Hindu can convert to any other religion when ever he wants. If there is no provision to welcome outsiders then there are no restriction to stop who wants to quit as well (in any hindu script). A non Hindu can practise Hindu way of life, no orthodox Hindu stops him. There are thousands of foreigners in India living the Hindu way of life under the guidance of any sage or a guru. No body tells them they have no right on moksha (nirvana); they are trying to achieve by hindu ways or they are less closer to a hindu god than a typical hindu. Can non Christian live a Christian's life without being converted, can non Muslim pay daily namaz to Allah without being Muslim. I do not think think so.
A non hindu can not jump into the continuity of Hindu tradition or value he wants to follow. In which cast he will be grouped in? Is it deliberate? No it is not deliberate. It's just the way it is. Such practises are very very old, have pretty sought out concept about spirituality and bussiness of God, were not under threat by outsiders when grooming/developing well in isolation.