Hey, you may be 15 but I'm not - less of the schoolyard stuff thanks
You make an interesting point - hard cash does wonders for architecture. There's no doubt that the money generated by colonialism aided these countries in creating their built environment. As to whether it is the sole factor I don't know.
In other countries in the past it tended to be the state or rulers of the day that built supposedly great architecture - in Enlightened Europe the cash was spread comparitively across the board and industry & commerce needed buildings. Combine cash, huge industries and 'enlightenment' - whatever your interpretation of that may be, and you've got, well, if not 'better' architecture, than at least a certain standard of design - and of course, tonnes of it.
It is the sheer amount of the stuff that defines these countries more than anything else.