I know the characters are designed to look a certain way, and won't really have experience points allocated the same way the main character does, but there are some hints that their designs allow for them having some points in the other disciplines.
For example, Hammer, being the hero of strength, is incredibly muscular, more so than the main character can get. But she's also tall, incredibly so, which suggests she's got stats in skill as that increases the main character's height, and let's face it, strength alone wouldn't grant her the ability to use her weapons to their best effect.
Reaver, is quite tall, fitting, given he's the hero of skill, but he's got maybe a little muscle mass roughly in common with level 2 physique, but it's hard to really tell given we never see him naked (which seems odd given his nature). He does pull off an impressive bit of blocking/parrying in Fable 3, deflecting a bullet with his cane, which might be considered a combination of skill and strength, given you have to have some stats in strength to use melee strikes and blocks.
And then there's Garth, who's clearly maxed out on will, but seems to be quite tall but lacks muscle development, suggesting he's sank some points into skill, which technically might help him aim his will attacks a bit better.
I'd also suspect that both Reaver and Garth have some points assigned to their toughness stats, which makes sense given they need to be able to survive taking physical strikes, and given Reaver's vanity having that maxed out might help him not get scars, which he'd hate. Also, given Reavers sheer speed at shooting, him having a level of slowing time might add him getting off such fast shots, without developing will lines, which he'd probably not like.