"queue debate about tools that hold your hands vs understanding what you are actually writing"
For a start, explain why, in Java, (int) Math.random() is a bug. A programmer that happens upon this thread, now knows "this is bad", but has no clue why. A tool will only make the programmer even more reliant on tools and IDEs, so this kind of bug will be eliminated, but the frame of mind that spawned it will live on.
Findbugs, the popular Java tool I linked to in another comment, explains the bug like this:
"A random value from 0 to 1 is being coerced to the integer value 0. You probably want to multiple the random value by something else before coercing it to an integer, or use the Random.nextInt(n) method."
That's about as good an explanation as you'd get from anyone.
The way I see it is this. Simple bugs like this happen because _human beings are flawed._ All it takes is a momentary lapse of concentration and you've put the cast in the wrong place in a method you don't write a test for because you're in a hurry, and all it's doing is generating a random number with a standard API so why bother? (Or it's something you wouldn't normally even test for, like assuming something is re-entrant when it isn't)
We're inevitably going to make a certain number of mistakes a day, and it's our duty to put systems into place that catch those mistakes before they cause any more damage than they should.
[queue debate about tools that hold your hands vs understanding what you are actually writing]
I wonder if they did the search for if (x = y) bug pre-gcc-4.x-warn what sort of numbers they would get.