ROFL. You crack me up with some of these threads... my two cents.
At it's most basic, women like to feel 'protected' and from an anthropological and physiological aspect, women desire to 'dovetail' well when in the throes of lovemaking. Hence, a man with certain chest - waist ratios will in general (barring strange skeletal frame exceptions) have a slight V shape. This is a natural counterweight to women's physiological predominant frame of most often having larger hip to waist ratios as part and parcel of being optimized to procreate and give birth to healthy children.
So, in general, a V shape is something that can often visually stimulate a woman with thoughts of 'climbing/ mounting' when in her equivalent 'heat' cycles (ovulation - as well as just being aesthetically pleasing - think Statue of David). Combine that with the protection element (being encapsulated in stronger arms than hers) is a general 'base level turn on' to the majority of women - I surmise.
Then there's all those non physical variables that come into play, but since you only asked about the physical I'll end it there.