jhg, laws don't change as fast as technology. Remember, really adequate bullets haven't been available all that long.
The next problem, from the standpoint of the wildlife folks, is knowledge among the .223 users: Not everybody yet realizes the difference between the varmint-style 50- and 55-grain bullets compared to the ones mentioned by Jack, above.
You're from BATFE? Come right in! I use all your fine products!