Oh, and here are some updated figures.
For year ending March 2013:
NLC revenue 55.9B rupee = ~US$927.6 million
TATA revenue 330.25B rupee = ~US$5.48 billion
Seems like that gap is getting bigger (from 3.9x to 5.9x).
Sources:
NLC Audited Accounts
TATA Power Audited Accounts
Note: 1 crore = 100 lahk