It might depend on your zone.
In the Euro zone, where such practice is supposed to be illegal, it is not common, but it happens regularly.
I still remember when Stardock, who was one of those few nice guys actively fighting the Dollar=Euro scam, decided to raise the pricing of all their games a couple years back, the day before a Steam sale as well.
Rockstar is a bit more upfront, raising sometimes their prices depending on their mood, not Valve’s agenda.
When it happens, it is funny how consistently Valve is blamed for such pricing fluctuation, as if publishers didn’t decide themself of the pricing of their games on Steam.