Per the Chicago Trib article below: "The league said 26 of the 30 Major League Baseball teams use some kind of flexible pricing system."
The use of dynamic pricing was put in place in such a wholesale practie because (as I understand it) teams were tired of losing business to the stub hubs and whatnot.
Bottom line: almost all teams adjust their prices, and they have done so in various ways throughout history.
Baseball teams get dynamic with ticket pricing - tribunedigital-chicagotribune
A's Ticket Pricing | Oakland Athletics
Astros Ticket Pricing | Houston Astros
Giants Ticket Pricing | San Francisco Giants