So I've been a bit confused regarding the exclusivity aspect of the 2 small/medium hull types in the research tree. They are listed as exclusive techs, however, some games I play both are exclusive, other games will allow me to lock both medium class hulls, sometimes just both small hulls, and a couple games have allowed me to unlock all four.

Is there an achievement (deed accomplishments were my first thought, but I really haven't come to anything conclusive) that you can accomplish to get access to both techs? I'd love to know because there's nothing I love more than a fully tech'd out fleet and I miss the complete ship models ever so much... I understand the tactical purpose of making these techs exclusive but I truly miss being able to fully upgrade my ships. It takes time to research these techs, can't that be enough of a sacrifice? CAN'T IT?!  O.O