Gamasutra posted a report with several developers bearing witness to the impact of Steam sales and how it does not devalue their games. Not only does the sale itself score them way more revenue than usual, but even when the price is back to normal it seems higher than usual sales are sustain for a few weeks.
Here are some of the examples quoted in the Gamasutra article:
"We find that we get several thousand percent increases in units and revenue on the days of the Steam sales, and unit sales are usually about double the normal for a few weeks after the sales are over," says Runic Games' (Torchlight) Max Schaefer.
"A lot of times we judge the success of a game -- and predict its sales -- by looking at its launch day numbers. Steam sales have made that delightfully impossible. Our launch day [for Bastion], which we viewed as very strong, is only our fifth best day of sales ever on Steam due to the power of the promotions we've had the opportunity to participate in," says Supergiant Games' (Bastion) Amir Rao.
"It's not uncommon for our partners to see [a] 10-20 times revenue increase on games they run as a 'Daily Deal.' Some titles really take off and see as much [as a] 70-80 times increase in revenue," says Valve's director of business development, Jason Holtman,
There is still fear that sales such as these run the risk of devalueing games longterm, but apparently sales only have positive effects for the developers in question.