There are a couple good, very exhaustive discussions on Otzi's bow and yew bows in general over on PP:
---http://paleoplanet69529.yuku.com/topic/17432#.Ve9zsO9RFgk
---http://paleoplanet69529.yuku.com/topic/14119/202lb-yew-warbow?page=9#.Ve9z8e9RFgl
Basically, Otzi's "bow" looks like it was made entirely of yew heartwood and has unusual grain orientation: it either has a decrowned back or, flipped the other way, does not follow a ring on the back. There are also no knocks: just pointed tips. The surface is not smoothed and shows many tools marks. Reproductions made with yew and using the same dimensions yield bows in the 160# range at 28" draw. Otzi was 5'-3" (63") tall and the "bow" is 1.82 meters long (71.65").
You decide if it was a bow or not. I think it's a goat-herders' stick, but that's me.