you recieve bonus from the highest stat, not from both (which is retarded, there isnt a single martial art that shouldnt benefit from both, tbh
Styg should probably key melee to both, maybe maul just to str).
I think you and Styg have the same general idea there, but the implementation differs. Melee benefits from both stats: STR increases damage depending on weapon type, DEX increases crit chance and also reduces AP cost for light weapons. Minmaxing str/dex isn't always the best choice for melee builds.
However, bonus to melee skill (which is a large factor in damage and precision) comes only from the highest stat. Why? Probably to keep things consistent, but getting that bonus from 2 stats would also be too much. Especially for some NPCs. Now, you might think that melee could be based on 50% STR 50% DEX and that would keep the overall system balance (althought that would not change anything in this case) but it would be a nerf to most melee players because they'd need more stat points to reach their old bonus. It would also be inconsistent, as the practical ceiling for this bonus would be lower than for any other skill.