Enones and hydrogenation Are enones resistant to hydrogenation? My solutions manual thinks so. 



I don't recall discussion regarding enones in my text. Nonetheless, could the resonance stabilization of the enone be preventing its hydrogenation? In that case, why is the alkene hydrogenated; both the carbonyl and the alkene are resonance-stabilized to some extent!
I read your question as asking why the C-C pi bond is reduced while the C-O pi bond is not. It appears to be possible to change the selectivity of hydrogenation based on the catalyst used (reference), but for simple palladium on carbon, reduction of alkenes (even conjugated to carbonyls) is much faster than an aldehyde or ketone. Coupled with complementary hydride reagents, which are selective for carbonyls, synthetic chemists can achieve the desired reduction without worrying about reaction of other reducible groups.