i've heard a few conflicting opinions too, 1 vet told me that if you get the bitch spayed before season 2/3 that there was evidence to suggest that the likelihood of ovarian cancer was reduced, another said that it didn't really make any difference!
both agreed that it was best practice to wait untill after the 1st season, and neither mentioned the risk you stated and the research i did on the net didnt mention that.
i do know that some owners i personally know have incontinence issues with some of the larger breeds following the op, my terrier (pat), has been absolutely fine on that score,