I decided to watch them closely to know the reasons behind this and my findings were very interesting. They say No at the right places but not at the expense of the overall user experience. Below are my little fundas of things they are doing right.
1. They said No to aerobridge
Using aerobridge at the airports is an extra expense to the airline. But using step ladder also adds extra effort to the airline eg more people to support wheel chair bound passengers. Coaches to ferry passengers from the terminal to the aircraft, but no airline can completely say no to it as there are instances when the aerobridge wont be available for use. And of course the not so great user experience.

The ramp you see here is their answer to an aerobridge. This would make the boarding process a little different for the user. They place one crew member at the start of the ramp and one at the turn. Its conversational. And yes they dont need extra people to support wheel chair bound passengers.
2. They said No to in-flight magazine
However they have a very interesting in-flight catalog of things they sell. Its like a magazine in itself. Its also their showcase of talent, mouthpiece to brag and take digs at competitors and yes to make money too. Sample the below shots.

My personal favorite is their Eat Spice, Drink Beer and Fly Indigo T Shirt ;-)
3. They said No to warm food
Warm food means more energy, aluminium foil packing etc. However their menu made it so irresistible to order. I ordered for a samosa and the miss Indigo said "We do serve samosa but its not warm. Is that Ok?" I showed a face but she smiled. I said fine.

She got the Samosa in an interesting packaging which made me smile.
4. They said No to water bottle
More weight to carry and unnecessary expense if given to people who really dont need water. They serve water from a jug to a paper cup.
5. They said No to Frequent Flying Program
The costs attached to run this program is eliminated which would help them to have the ticket prices low. Also no exclusive check in counters and no red (or blue) carpets; all the passengers are same for them. Also they don't have to deal with the whims and fancies of the "rich show off" members. I know as I have friends working in the airline industry.
6. They said No to different aircraft models
All their aircrafts are of the same make and model. So no different types of pilots, engineering expertise, training programs etc. Also brand new aircrafts that will bring down maintenance costs.
7. They said NO to delays, ahem in a clever way
Now this is debatable but I dont find a problem with it. The flying duration of Indigo flights are communicated as little more than other airlines coz it includes the slight delay that occur due to traffic congestion or something beyond their control. This is smart as it allows them to be percieved as on time and no one seems to be complaining. Eg Do a search from BLR to BOM on any travel site and look at the flying duration of Indigo flights.