Actualy you are wrong about the multiplier on the compound bow. The mechanical advantage offered by a compound bow is actualy quite ingeneous. Remember that you still need to pull the string back and that force is what is used to propel the arrow. However, once the string is pulled back to the bows "Sweet Spot", the force required to hold it there is reduced by a factor of 10 (I think, I'm not sure the actual factor). This means that while it may take 75lbs of pull strength in your arm to get it to ready, you only need to deal with 7-8 pounds while you aim. This help mostly in a steady aim and lower arm fatigue.
I was thinking the STR multiplier from the perspective that the greater maximum pull and ease of holding would permit a character to use a much stronger pull bow. It is after all much easier to exert more force for a short period of time, but I was also under the impression that the compound bow setup also reduced the difficulty of drawing the bow string back.
Yes, I know the difference between compound and composite bows (not that I could expect you to psychically know that! )- but I wasn't refering to the bow in that link. I was refering to the draw-lock device itself. You can see the device much better in this pic from the site- "How to use" illustration. A locking bar and trigger device like that could be fitted to any kind of bow. I did a research article on crossbows way back in high school and found a mgazine article that showed you how to build your own. The Draw-Loc webpage was just the easiest one I could find to show it.
It was not entirely clear from your statement if you did, but it was not the whole reason I mentioned that. As I pointed out a traditional bow/composite bow can't be left strung for long periods of time without ruining it. So the device you pointed out would really be of at best limited usefulness. Compound bows are in fact are almost never unstrung, which is one of the reasons why a device like that is useful with one.
The foot pull that was show in the illustration reminds me of There were some bows used that were in fact pulled with the whole body, with archer lying down, the feet braced against the bow and holding on to the bow string with one's hands, but I think they were only used in limited circumstances since its not the best position to be in in combat.
I just find the whole idea of a "Strength Crossbow" to be essentially an oximoron. Since the bowman's strength really only affects reloading speed and it's the preset power of the crossbow that determines the damage.
I really think in fact that there shouldn't be "Mighty Bows" at all. The strength damage modifiers should be an inherent part of using a bow, not some extra optional feature. I suspect the reason it is done the way it is, probably comes down to more game balance mechanics than any logical reason. Simply because of the significantly increased lethality of an archer with the added damage gets.
If you really wanted a crossbow that did more damage, which is what the argument really comes down to. I would say require exotic materials or something similar to that for the damage bonus. Adamantine crossbows get an extra +4 damage due to their stronger bows or Mythril crossbows get +2 damage and take 1 phase/action less to reload due to the light weight and flexibility of their bows.
)- but I wasn't refering to the bow in that link. I was refering to the draw-lock device itself. You can see the device much better in this pic from the site- "How to use" illustration. A locking bar and trigger device like that could be fitted to any kind of bow. I did a research article on crossbows way back in high school and found a mgazine article that showed you how to build your own. The Draw-Loc webpage was just the easiest one I could find to show it. 
