Hi diverdil!
It's true, it doesn't come down to some fancy blend of 50 different spices, but to the knowledge of what, when and, most importantly, why. Actually, I like to use less spices, but the right ones.
Turmeric adds colour, that's right, but it gets used for its health and preservative properties, too. It also balances the flavour. Coriander will thicken the sauce, and adds some unique fruity flavour (besides anti-inflammatory properties). Fenugreek seeds are actually a sort of legumes, but get often used as a spice because of their strong flavour (and health properties, too). They prefer kashmiri chili powder in some dishes (tandoori, e.g.), because it also adds a nice, earthy flavour. Chilis provide you also with vitamin C (but are no traditional indian spice). Garam masala is based, you could say, like indian spicing in general, on the ayurvedic system. (the six different tastes, and so on) Cloves and cinnamon oil is said to kill all bacteria.
Indian desserts are full of sugar, because this will prevent them going off too fast. (especially in that climate) But I prefer jaggery, brown sugar, palm sugar or honey, because they all add flavour and body, while ordinary white, refined sugar will just add sweetness. (unrefined sugars are healthier, too) That wasn't part of your original question, although it somehow shows what I mean (:
Greetings!