Sure the 3175kg limit is open for discussions. But i think it's the wrong way at first to design an a/c and to discuss the EASA/FAA weight limits on a second stage due to weight problems of the ship.
The different BK117 versions including EC 145 (BK117 C2 by certification) and in future the brand new EC145 T2 are riding on many points on the old grandfather certification of the BK 117 A. EC have only to certify the new parts. Thats a big difference while certification to a fully new designed ship like the MD900 and it's not an unimportant point why EC goes along this way.