From last week's Mayor's Question Time:

http://mqt.london.gov.uk/mqt/public/...on.do?id=30225

Question by Caroline Pidgeon

Why is it not possible at present to get Gold Card or Network Railcard
benefits in conjunction with Oyster PAYG? How many people would
benefit from this? Do you have any plans to introduce this?


Answer by Boris Johnson

Railcard schemes are provided by the Train Companies, generally on a
national or regional basis, and TfL does not hold any statistics
regarding holder numbers.

Following discussions with Companies, TfL hopes to introduce PAYG Gold
Card benefits from the end of May. The Train Companies imposed
conditions on their Network Railcard scheme some years ago, which
means that it only provides limited discounts for travel within
London. The Train Companies continue to wish to focus this card on
their regional leisure market, and have indicated that they do not
wish to offer PAYG benefits for travel on their services within
London.