exactly greg; i have a "curry cookbook" that is divided by cultures (trinidadian, south indian, japanese, pakistani, etc.) and there is a section "british" that includes things like chicken tikka masala.
truth is, most things we view as "indian food" were created or modified heavily by the colonial presence. vindaloo, for example, is actually an attempt to make a portuguese dish (from goa, the portuguese colony) and is supposed to be made with pork. "curries" and whatnot usually include things like tomato, hot pepper, etc. which were not in india thousands of years ago at all! so it's not like chicken tikka masala is TOTALLY NOT INDIAN and rogan josh is TOTALLY INDIAN. everything is just a hodgepodge of influences.