I have heard that you can damage the master cylinder seals by driving the piston beyond its normal travel using the "pump the brake pedal" method on this forum in the past. While I believe it is possible and even likely if there are corrosion products building up in the master cylinder, I do not think it is normal. If you flush the system regularly with every pad changeout, or every two years as recommended by the manual for the car, and use good quality brake fluid this issue should not present a problem.
I have yet to replace a brake master cylinder in more than thirty years of owning cars I have driven to more than 250,000 miles, and regularly changed brake fluid with pads. I do not think I am lucky or a statistical anomoly. Corrosion only happens when you let brake fluid get laden with moisture. If you do not let that happen, there is no means to initiate corrosion of the parts. Brake fluid is cheap, and it should not be left to rot away the calipers and master cylinder.
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)