PS Hacker and amateur of Blender & game coding here.
Without the unoptimized shadows of CS, you can run more than 5 000 000 polygons on a low end computer on PS.
Plus, with the current computers, game engines can handle more than thousands of polygons for simple items without problems (that is, if you forget unoptimized shaders)
Most recent games have weapons that have more than 1000 polygons, going up to more than 10000. (Half Life 2 has for example about 2000 polygons for the simple pistol, but that's a FPS)
But even if our limits with polycount gets pushed off higher and higher, it's still a good practice to keep the poly count as low as you can.
The decimate modifier might help you in that in Blender, but it can lead to some mesh glitches, so be sure to check everything by yourself in edit mode.
You used too much polygons because you tried to give the bow a smooth look with only vertices, but shaders have a huge part in making something smooth or not
. For example, click the smooth shading in the toolbox.
I would say that for a game, this bow should have like between 500 and 5000 polygons, depending on the game engine, the target audience, and if you're using a lot of high res models at the same time. For PS using CrystalSpace, <1000 polygons is good.