The way I see it, Aliens are all about fear first and foremost, and the idea of reproduction this way just makes them scarier. It's not like this'll be the first time that something that didn't exist previously suddenly exists. Ridge-Head Aliens, the concept of taking DNA from hosts, a Queen, none of these things were part of the original Alien, and yet they quickly became accepted. People can say that these things don't mess with the continuity because they can be explained, but no matter how you look at it, any addition can be explained somehow, and while many of you guys are pissed about it now, you won't be by the time a few more Alien films have been cranked out.
It'll become an accepted part of continuity in time, and will have it's explanation.