Since as far as I can tell, Finessable doesn't exist as an actual ability and it wasn't explained on-page: in-game it allows you to use your Dexterity score for attack rolls made with a weapon as long as you have the Weapon Finesse feat, even if it wouldn't ordinarily qualify. Bit on the nose, but Timely really wanted to make sure it was clear. ;)
Some might argue this is a bit of a waste of an ability, but hey, if you can get it for free.
To me, the funny thing is NOT using Dexterity (or a similar stat) for "to hit" rolls in the first place. While Strength still matters, it determines how much force is behind the attack, not your ability to actually hit with the attack. Ranking of Kings being this otaku's current example of this. Spoiler for Episode 2: The main character, Prince Bojji, pretty quickly establishes he has great speed and hand/eye coordination... but doesn't have the strength behind his attacks do to any serious damage.
Now, I think D&D has pretty much always handled it with Strength being the main one behind hitting with a weapon. I haven't played a lot of different RPG systems, but out of them... yeah, D&D was the only one like that. GURPS uses Dexterity as the go-to for combat oriented skills. I think Old World of Darkness and West End Games Star Wars were similar, if not the same.
Author Notes:
Since as far as I can tell, Finessable doesn't exist as an actual ability and it wasn't explained on-page: in-game it allows you to use your Dexterity score for attack rolls made with a weapon as long as you have the Weapon Finesse feat, even if it wouldn't ordinarily qualify. Bit on the nose, but Timely really wanted to make sure it was clear. ;)
Some might argue this is a bit of a waste of an ability, but hey, if you can get it for free.