Originally Posted by zkzkz

a) promotions that require that you use a code or book in a certain way are useful because it allows price discrimination -- you only cut the price for the people who cared about it enough to find and use the discount. Sure a small discount only has a small effect but there are always some people who are on the edge and they might have had a fare on another airline that was $20 cheaper.

b) The earlier promotion? You mean the extravelganza thing? Miles promotions work great because business travelers can spend more employer $$ on a more expensive fare that rewards them with bonus miles. It gets to the heart of why FF programs were invented and why they work. (And why they wouldn't be allowed if they weren't so entrenched...)

Also, unless you're paying extra for last-minute or specific (*cough* upgradable *cough*) fares $25 each way is a bit more than "2-5% at most". Flights to LHR from the east coast are typically $700-800 so it's more like 6-7%, assuming it's good on cheap T+ fares.