Alloy framed guns will all fail eventually...the question is when. This is because of the material properties of aluminum alloys which does not have an endurance limit like steel.
Most people put less than a hundred rounds a year through their guns so we don't get a lot of feedback in the 10,000 and up range.
It is possible that 30,000-40,000 is entering the danger region for that particular CZ frame.
Tanfoglio frames are known to crack at much lower numbers...especially in the heavier calibers, like 45mm and 10mm. Even Sigs have seen frame failures.
Most people, would never have to be concerned with these kinds of failures because they will never put this number of rounds through their guns.
FYI, at current prices, that number of rounds cost $7,000-$8,000 dollars (for a 9mm.) The $200 dollar frame is a much smaller cost in the grand scheme of things.
Woops: Corrected by Warder. Thinking of other CZ's that have alloy frames. Stand by the rest of my statement, however that this won't occur for 99.9% of people even if it is the fatigue limit of the frame.