Also, somewhere in all the Star Trek watching and reading I've done the past 30 years, I remember something about the Romulans having a habit of raping the male and females prisoners for the purpose of creating a baby. The guy prisoners would knock up a Romulan babe, the female prisoners would of course get preggers. The baby is brought to term in both cases and displayed to the prisoner and then, only then, is the prisoner killed. The baby is usually kept alive though. This is especially horrific for the Vulcans because of their honor or whatever, but was also used to explain the whole Romulan Tasha Yar thing in Next Gen.
So this could explain why so many Romulan halfbreeds exist in the Trekverse.