some other points in favour of trains:
1. you have to reach airport 1-2 hours before flight departure. Waiting in the security and check-in lines are excruciating. On the other hand, you can reach the station 5 minutes before train departure. No ticketing nonsense.
2. Travel time to airport is definitely not the same as travel time to a railway station, since stations are usually located in the middle of the city. Not only that, you will be charged very highly for travel to airport - all the auto/taxi drivers make a lot...
more... of money from airport passengers.
3. Vendors at airports give you bad quality tea/snacks at a minimum cost of Rs. 20, and the the cost goes as high as Rs. 100.
On the whole, take a train, relax, reflect, meditate, chat with co-passengers, have a small vacation. Rushing from Delhi - Mumbai - Chennai, your whole life will be over before you realize it.